This growing list attempts to pull together a list of the various Great War abbreviations that were used.

The list has been complied from a variety of sources: UK, Australian, Canadian & New Zealand sources.

"G" General Staff.
"Q" Quartermaster's Branch of the Staff.
1914 ST.  1914 Star
1914 ST.C.  1914 Star And Clasp
A T serum Anti Tetanus Serum
A" Administrative Staff.
AA Anti-Aircraft
AA Army Act
AA & QMG Assistant Adjutant And Quartermaster General
AAG Assistant Adjutant General.
AAMC Australian Army Medical Corps.
AASC Anti-Aircraft Searchlight Company
AASS Anti-Aircraft Searchlight Section
AB  Army Book
ABPO  Advanced Base Post Office
ACC  Army Cyclist Corps
ACG  Assistant Chaplain General
ACI  Army Council Instruction
AD  Artillery Depot
ADAPS Assistant Director Army Postal Services
ADC  Aide De Camp
ADGT  Assistant Director-General Of Transportation
Adj Adjutant
ADL  Assistant Director Of Labour
ADLR  Assistant Director Of Light Railways
adm Admitted
ADMS  Assistant Director Medical Services
ADO Administrative Dental Officer.
ADOS  Assistant Director Ordnance Services
ADRT  Assistant Director Railway Traffic
ADS Advanced Dressing Station
ADTN  Assistant Director Transportation
ADVS Assistant Director Veterinary Services
AEC Area Employment Company
AF Army Form
AFA Army Field Artillery
AFA Australian Field Artillery
AG Adjutant General
AGS Army Gymnastic Staff
AIF Australian Imperial Force
AIS Assistant Inspector Of Searchlights
ALH Australian Light Horse.
AM Issued To Air Ministry For Disposal To Man
AMC   Army Medical Corps  
AMC   Australian Army Medical Corps.
AMFO Assistant Military Forwarding Officer
AMLO Assistant Military Landing Officer
AMO Administrative Medical Officer
AMS Army Medical Service.
AMS Assistant Military Secretary
ANZAC Australian and New Zealand Army Corps.
AO Army Order
AOC Army Ordnance Corps
AOD Army Ordnance Department
AP Armour Piercing (Ammunition)
APC Army Pay Corps And Assistant Principal Chaplain
APM Assistant Provost Marshal
APO Army Post Office
AQMG Assistant Quartermaster-General
ARD Alberta Regimental Depot
ARD Alberta Reinforcement Depot
ARMW Army Reserve Munition Worker
ARP Ammunition Refilling Point
ARS Advanced Regulating Station
ASC Army Service Corps
ASD Army Schools Department
ASH  Argyll & Sutherland Highlanders 
ASO Area Searchlight Officer
ASP Ammunition Sub-Park
AT Army Troops
ATS Antitetanic Serum.
att'd Attached
auth Authorized, Authority
AVC Army Veterinary Corps
AWL Absent Without Leave
B.I.P. Bismuth, Iodoform, Parolin (paste).
B.o.T.  Issued To Board Of Trade For Disposal To Man
B.R.P. Bearer Relay Post.
BAC Brigade Ammunition Column
BAPO Base Army Post Office
Batt'n, Bn Battalion
BC  Battery Commander/Commandant
BCA  Battery Commander's Assistant
BCRD British Columbia Regimental Depot
Bdmr  Bandmaster
BEF British Expeditionary Force
BG  Broad Gauge (Railway)
BGGS  Brigadier-General General Staff
BGRA  Brigadier-General Royal Artillery
BL  Breech Loading
BLC  Breech Loading  Converted
BM  Brigade Major
BMBDR  Bombardier 
BNM Athens  British Naval Mission To Greece
BOR  British Other Rank
BRCS British Red Cross Society
BSM  Battery Sergeant-Major
Bty Battery
BWI  British West Indies Regiment
BWM British War Medal
By A.M.  Issued By Air Ministry (For service in RAF)
By B.o.T.  Issued By Board Of Trade (For service in Merchant Service)
By W.O.  Issued By War Office (For service in Army)
C. of P.  Commissioner Of Police
CADC Canadian Army Dental Corps
CAMC Canadian Army Medical Corps
CAMH  Cameron Highlanders 
CASC Canadian Army Service Corps
Cav Cavalry
CB Confinement To Barracks (Punishment)
CB Counter Battery
CBD Canadian Base Details
CBSO  Counter-Battery Staff Officer
CC  Confined To Camp (Punishment)
CCAC Canadian Casualty Assembly Centre
CCCC Canadian Corps Composite Company
CCCC  Cape Colony Cyclist Corps
CCD Canadian Convalescent Depot
CCD Commander Of Coast Defences
CCRA  Corps Commander Royal Artillery
CCRC Canadian Corps Reinforcement Camp
CCS Casualty Clearing Station
CDAC Canadian Divisional Ammunition Column
CDD Canadian Discharge Depot
CDS  Corps Dressing Station
CE Canadian Engineers
CE  Chief Engineer
CEF Canadian Expeditionary Force
CEPC  Chief Engineer Port Construction
CERD Canadian Engineer Reinforcement Depot
CF Chaplain To The Forces
CFA Canadian Field Ambulance
CFA Canadian Field Artillery
CFC Canadian Forestry Commission
CFC Canadian Forestry Corps
CGA Canadian Garrison Artillery
CGH Canadian General Hospital
CGM  Conspicuous Gallantry Medal 
CGR Canadian Garrison Regiment
CGS Chief of the General Staff.
CHA Commander Heavy Artillery
CHA Corps Heavy Artillery
CHDAVC  Convalescent Horse Depot Army Veterinary Corps  
C-i-C Commander In Chief
CID Committee Of Imperial Defence
CIGS Chief Of The Imperial General Staff
CL Casualty List
CLC  Chinese Labour Corps
CLH Canadian Light Horse
CLLE  Charger-Loading Lee-Enfield Rifle
CLLM  Charger-Loading Lee-Metford Rifle
CLRO Corps Light Railway Officer
CMDS Corps Main Dressing Station.
CME  Chief Mechanical Engineer
CMGC Canadian Machine Gun Corps
CMO  Court-Martial Officer
CMP  Corps Of Military Police
CMR Canadian Mounted Rifles
CO  Commanding Officer
CO  Conscientious Objector  
Cofl Court Of Inquiry
Com Command
Conv Convalescent
COO  Chief Ordnance Officer
CORD Central Ontario Regimental Depot
Coy Company
CP  Censorship & Publicity
CPDI Chronic Pulmonary Disease, Ideterminate.
Cpl Corporal (Rank)
CQMS Company Quartermaster Master Sergeant
CRA Commander, Royal Artillery
CRCE  Chief Railway Construction Engineer
CRCR Canadian Reserve Calvary Regiment
CRE  Commanding Royal Engineers
CRO  Corps Roads Officer
CRT Canadian Railway Troops
CSIC  Cadet School Infantry Company
CSM Cerebro-Spinal Meningitis
CSM Company Sergeant-Major
CT Communication Trench
CVBC Cape Volunteer Bearer Corps
D of A  Director Of Artillery
D Rlys  Director Of Railways
D.  Discharged With Disgrace
DA  Divisional Artillery
DA & QMG  Deputy Adjutant And Quartermaster General
DAA  Director Of Army Accounts
DAAG  Deputy Assistant Adjutant General
DAC Divisional Ammunition Column.
DAC Divisional Ammunition Company
DACG  Deputy Assistant Chaplain General
DAD Roads  Deputy Assistant Director Of Roads
DAD Sigs  Deputy Assistant Director Of Signals
DADAPS  Deputy Assistant Director Army Postal Services
DADGR&E  Deputy Assistant Director Of Graves Registration And Enquires
DADGT  Deputy Assistant Director-General Of Transportation
DADL  Deputy Assistant Director Of Labour
DADMS  Deputy Assistant Director Medical Services
DADMS  Deputy Assistant Director of Medical Services.
DADOS  Deputy Assistant Director Ordnance Services
DADPS  Deputy Assistant Director Postal Services
DADRT Deputy Assistant Director Railway Traffic
DADS  Deputy Assistant Director Supplies
DADT  Deputy Assistant Director Transport
DADW  Deputy Assistant Director Of Works
DAG  Deputy Adjutant General
DAH Disordered Action of the Heart (Medical)
DAMS  Deputy Assistant Military Secretary
DAP  Divisional Ammunition Park
DAPC  Deputy Assistant Principal Chaplain
DAPS  Director Of Army Postal Services
DAQMG  Deputy Assistant Quartermaster General
DBC  Director Of Barrack Construction
DCIGS  Deputy Chief Of The Imperial General Staff
DCM Distinguished Conduct Medal
DCM  District Court-Martial
DD S and T  Deputy Director Supplies And Transport
DD Sigs  Deputy Director Of Signals
DDAPS  Deputy Director Of Army Postal Services
DDGMR Deputy Director-General Military Railways Or Movements And Railways
DDGT  Deputy Director-General Of Transportation
DDIWT  Deputy Director Inland Waterway Transport
DDMS  Deputy Director Medical Services
DDOS  Deputy Director Ordnance Services
DDRT  Deputy Director Railway Traffic
DDS Director of Dental Services.
DDTN Deputy Director Of Transportation
DDVS  Deputy Director Veterinary Services
DDW  Deputy Director Of Works
DEOS  Director Of Equipment And Ordnance Stores
DFC  Distinguished Flying Cross
DFS Director Of Financial Services
DFW  Director Of Fortifications And Works
DGAMS  Director-General, Army Medical Services
DGAVS  Director-General, Army Veterinary Services
DGMS Director General of Medical Services.
DGNS  Director-General National Service
DGO Divisional Gas Officer
DGTF  Director-General Of The Territorial Force
DIL  Dangerously Ill List
dis Discharged
Div Division
DIWD  Director Inland Waterways And Docks
DIY Derbyshire Imperial Yeomanry
DLI  Durham Light Infantry 
DLR  Director Of Light Railways
DM  Director Of Mobilisation
DMH Director of Military Hospitals,
DMO  Director Of Military Operations
DMS  Deputy Military Secretary
DMS  Director Of Medical Services
DMT Director Of Military Training
DND Ottawa  Department Of National Defence, Ottawa
DNTO  Divisional Naval Transport Officer
DO Daily Order (Of A Unit)
DOCLI  Duke Of Cornwalls Light Infantry 
DofW Died Of Wounds
DORA  Defence of the Realm Act.
DORE  District Office Royal Engineers
DOS Director Of Ordnance Services
DOWWR  Duke Of Wellingtons West Riding Regt 
DP Drill Purpose
DPS Director Of Personal Services
DPW Director Of Prisoners Of War
DQMG Deputy Quartermaster-General
DR Despatch Rider
DRF Depression Range-Finder
DRG&E  Director Of Graves Registration And Enquires
DRIM Director, Royal Indian Marine
DRLS  Despatch Rider Letter Service
DRO  Director Of Recruiting And Organisation
DRS Divisional Rest Station.
DRT  Director Railway Traffic
DSC  Distinguished Service Cross (Naval)
DSD  Director Of Staff Duties
DSM  Distinguished Service Medal (Naval)
DSO  Distinguished Service Order
DSQ  Director Of Supplies And Quartering
DTM  Director Of Transport And Movements
DTMO  Divisional Trench Mortar Officer
DTN  Director Of Transportation
DUPS.  Duplicates Issued
Dvr Driver
DW  Director Of Works
E&M  Electrical And Mechanical
EBD Employment Base Depot
EBSVR  East Bengal State Volunteer Rifles
EEF  Egyptian Expeditionary Force
EFC  Expeditionary Force Canteen
EinC Engineer In Chief
ELC  Egyptian Labour Corps
emb Embarked
EMO  Embarkation Medical Officer
EORD Eastern Ontario Regimental Depot
ET Early Treatment (V.D.).
F.  Forfeited ("R"(Run) Or "D"(Discharged with disgrace))
FA  Field Artillery 
FANY  First Aid Nursing Yeomanry
FAO  Forward Area Officer (Light Railways)
FAU  Friends Ambulance Unit
FGCM  Field General Court-Martial
FLC Fijian Labour Contingent (Later Corps)
FOO Forward Observation Officer
FP Field Punishment
FPO Field Post Office
Frac Fractured
FSC Field Survey Company
FSL Field Searchlight
FSM Field Service Manual
FSR Field Service Regulations
FWD Four Wheel Drive
GC Badge Good Conduct Badge
GCM General Court-Martial
Gen General
GHQ General Head Quarters
GMP Garrison Military Police
Gnr Gunner
GOC General Officer Commanding
GOCinC  General Officer Commanding-In-Chief
GOCRA General Officer Commanding Royal Artillery
GRC Graves Registration Commission
GRO General Routine Order
GRU Graves Registration Unit
GS General Service And General Staff
GS General Service.
GSP General Staff Officer
GSW Gunshot Wound
HA Heavy Artillery
HAC  Honourable Artillery Company 
HAR Heavy Artillery Reserve
HARG Heavy Artillery Reserve Group
HBMGC  Heavy Branch Machine Gun Corps (Later Tank Corps)
HE High Explosive
HLI  Highland Light Infantry 
HMS His Majesty'S Service
HMT His Majesty'S Troopship
Hosp Hospital
How Howitzer
HPD Home Postal Depot
HQ Headquarters
HS Home Service
HSC Hospital Ship Case (Medical)
HT Horse Transport
HV High Velocity
IA Indian Army
IAF Independent Air Force
IE Illegal Enlistment
IF Imperial Force 
IGC Inspector General Of Communications
IGS Imperial General Staff.
IGT Inspector General Training
IGT Inspector-General Of Transportation
IHL Imprisonment With Hard Labour
ILP Independent Labour Party (political - opposed to the war, defended the dependents of soldiers)
IMS Indian Medical Service.
inv "wd" Invalided Wounded
IO Intelligence Officer
IOM Inspector Of Ordnance Machinery
IOR Indian Other Rank
IS Inspector Of Searchlights
IW&D Inland Waterways And Docks
IWGC  Imperial War Graves Commission
IWT  Inland Water Transport
JAG  Judge Advocate General
KAR  Kings African Rifles 
KIA Killed In Action
KORL  Kings Own Royal Lancaster 
KOSB  Kings Own Scottish Borderers 
KOYLI  Kings Own Yorkshire Light Infantry 
KR King's Regulations
KRRC  Kings Royal Rifle Corps 
KSLI  Kings Shropshire Light Infantry 
L/C or L/Cpl Lance Corporal
L/CPL  Lance Corporal 
LEE London Electrical Engineers
LEG.REP.  Legal Representative
LG (Lon. Gaz.) London Gazette
LIR  London Irish Rifles 
LMB Light Mortar Battery
LO Liaison Officer
LOC Lines of Communication.
LofC Lines Of Communication
LR Local Reserve
LRB  London Rifle Brigade 
LSH Lord Strathcona's Horse (Royal Canadians)
M&D Medals & Decorations
MAC Motor Ambulance Convoy
MB Medical Board
MC Military Cross
MCV Mixed Catarrhal Vaccine.
MD Military District (Or Depot)
MDS Main Dressing Station
MEF Mediterranean Expeditionary Force
MFD Military Forwarding Department
MFO Military Forwarding Officer
MFP Military Foot Police
MGC Machine Gun Corps
MGGS Major General General Staff
MGO Master-General Of The Ordnance
MGRA Major General, Royal Artillery
MGS Machine Gun School
MIA Missing In Action
MID Mentioned-In-Despatches
Mil Military
Miss Missing
MLO Military Landing Officer
MM Military Medal
MMGC Motor Machine Gun Corps
MML Manual Of Military Law
MMP Military Mounted Police
MO Medical Officer.
MPI Mean Point Of Impact
MPSC Military Police Staff Corps
MRD Manitoba Regimental Depot
MS Military Secretary
MSM Meritorious Service Medal
MT Mechanical Transport
MTASC Motor Transport Army Service Corps.
MVC Motor Volunteer Corps
MVS Mobile Veterinary Section
NACB National Army Catering Board
Nav.Rep.  Naval Representative, Commonwealth Of Australia
NCC Non-Combatant Corps
NCF No Conscription Fellowship
NCI Napthalin, Camphor, Iodoform (powder).
NCO Non Commissioned Officer
NLR  North Lancs Regt 
NO Navy Office, Wellington, Etc.
NORTHF  Northumberland Fusiliers 
NSRD Nova Scotia Regimental Depot
NTO Naval Transport Officer
NYD Not Yet Determined
NYD Not yet Diagnosed
NYD Not Yet Diagnosed (Medical)
NYDN Not Yet Diagnosed Nervous (Medical for suspected shell shock)
NZANS New Zealand Army Nursing Service.
NZDC New Zealand Dental Corps.
NZE New Zealand Engineers.
NZEF New Zealand Expeditionary Force.
NZFA New Zealand Field Artillery.
NZGH New Zealand General Hospital
NZMBFA New Zealand Mounted Brigade Field Ambulance.
NZMC New Zealand Medical Corps.
NZMR New Zealand Mounted Rifles.
NZPS New Zealand Permanent Staff.
NZRB New Zealand Rifle Brigade.
NZSC New Zealand Staff Corps.
OBLI  Ox & Bucks Light Infantry 
OC Officer Cadet
OC Officer Commanding
OC Officers Clerk
OCB Officer Cadet Battalion
OLI  Oxford Light Infantry 
OMFC Overseas Military Forces Of Canada
OR Other Rank
ORS Orderly Room Sergeant
OS Overseas
OTC Officers Training Corps
P & BT Physical And Bayonet Training
P&S Plaque & Scroll (Memorial)
PB Permanent Base (Medical)
PBI Poor Bloody Infantry (Colloquial)
PC Principal Chaplain (Non Church Of England)
PDMS Principal Director of Medical Services.
PM Provost Marshal
PMO Principal Medical Officer.
Pnr Pioneer
PNTO Principal Naval Transport Officer
POW Prisoner of War.
PPCLI  Princess Patricia's Canadian Light Infantry 
PRC Parliamentary Recruiting Committee
pres Presumed
Proc Proceeded
psc Passed Staff College
Pt. II O Part Ii Orders
Pte Private
PU Permanently Unfit (Medical)
PUO Pyrexia Of Unknown Origin
PVT  Private 
QAINS Queen Alexandra's Imperial Nursing Service.
QF Quick Firing
QM Quartermaster.
QMAAC Queen Mary's Army Auxiliary Corps
QMG Quarter Master General
QMS Quartermaster Sergeant
QRD Quebec Regimental Depot
Qs Qualified For Staff
QVR  Queen Victorias Rifles 
R.  Run
RA   Royal Artillery
RAF Royal Air Force
RAFA Royal Australian Field Artillery
RAGA Royal Australian Garrison Artillery
RAMC  Royal Army Medical Corps.
RAOC  Royal Army Ordnance Corps
RAP Regimental Aid Post
RASC  Royal Army Service Corps
RCD Royal Canadian Dragoons
RCE Railway Construction Engineer
RCHA Royal Canadian Horse Artillery
RCO Railway Control Officer
RCR Royal Canadian Regiment
RDC Royal Defence Corps
RDF  Royal Dublin Fusiliers
RE  Royal Engineers
REGT  Regiment
rem Remained
REPS Royal Engineers Postal Section
rept Reported
Res Reserve
RES.LEG.  Residuary Legatee
RFA Royal Field Artillery
RFB Reported From Base
RFC Royal Flying Corps
RGA Royal Garrison Artillery
RH Railhead
RHA Reserve Heavy Artillery
RHA Royal Horse Artillery
RHG  Royal Horse Guards
RIF  Royal Irish Fusiliers
RIFB  Rifle Brigade
RINSKF  Royal Inniskilling Fusiliers
RIR  Royal Irish Rifles
RM Riding Master
RM  Royal Marines
RMA  Royal Marine Artillery
RMF  Royal Munster Fusiliers
RMLC Royal Marine Labour Corps
RMLI Royal Marine Light Infantry
RMO Regimental Medical Officer
RN  Royal Navy
RNAS Royal Naval Air Service
RND Royal Naval Division (63 Div)
RNDH  Royal North Devon Hussars
RNR  Royal Naval Reserve
RNVR  Royal Naval Volunteer Reserve
RO Recruiting Officer
ROD Railway Operating Division
ROO Railway Ordnance Officer
ROYF  Royal Fusiliers
RP Refilling Point
RP Regimental Police
RP Rules Of Procedure
RSF  Royal Scots Fusiliers
RSM Regimental Sergeant-Major
RSO Railhead Supply Officer
RTC Reserve Training Centre
RTC Returned To Corps
RTE Railway Transport Establishment
RTO Railway Transport Officer (Later Railway Traffic Officer)
RTU Returned To Unit
RWF  Royal Welsh Fusiliers
S Service
S.  Self (Ie To The Man Himself)
SAA Small Arms Ammunition
SANLC South African Native Labour Corps
SB Stretcher Bearer.
SC Staff Captain
SCF Senior Chaplain To The Forces
SCRF  Scottish Rifles
SD Staff Duties
SEAFH  Seaforth Highlanders
SEF Siberian Expeditionary Force
SGS Surveyor-General Of Supply
SGT  Sergeant
SHLI  Shropshire Light Infantry
SIW Self-Inflicted Wound
SJT Serjeant
SLI  Somerset Light Infantry
SLR Superintendent Of Light Railways
SMLE Short Magazine Lee-Enfield
SMO Senior Medical Officer.
SOP Standard Operating Procedures
SOS Struck Off Strength (of a unit)
SP Strongpoint
Spr Sapper
SPT Sportmen's Battalion Royal Fusiliers
SR Special Reserve
SRS Sound Ranging Section
SS Steamship
SSM Squadron Sergeant Major (Cavalry)
ST.  1914-15 Star
Staty Stationary (Hospital)
STK Stockbroker's Battalion Royal Fusiliers
SW Shrapnel (Shell) Wound
SWB  South Wales Borderers
TAB Typhoid, Paratyphoid A. and B. (Vaccine).
TAT Temporary Ambulance Train
TB Temporary Base (Medical)
TC Tank Corps
TCO Train Conducting Officer
TDO Telephone Dug-Out
TEE Tyne Electrical Engineers
TF Territorial Force
TM Trench Mortar
TMB Trench Mortar Battery
TO Transport Officer
TOS Taken On Strength (Of A Unit)
Tpr Trooper
TR Training Reserve
trans Transferred
TRB Training Reserve Brigade
TSM Troop Sergeant Major (Cavalry)
TV Typhoid Vaccine.
UDC Union Of Democratic Control (political - campaigned for a negotiated peace)
UNIV.LEG.  University Legatee
unk Unknown
V.  Victory Medal
VAD Voluntary Aid Detachment
VADGS Voluntary Aid Detachment General Service
VC Victoria Cross
VD Venereal Disease.
VO Veterinary Officer
VTC Volunteer Training Corps
w,{w) Wounded
W.O.  Issued To War Office For Disposal To Man
WAAC Women's Army Auxiliary Corps (Later QMAAC)
WD War Department
WE War Establishment
WIR West India Regiment
WO War Office
WORD Western Ontario Regimental Depot
WSR  West Surrey Regt
WWCS Walking Wounded Collecting Station
YCV Young Citizen Volunteers (14th Battalion, Royal Irish Rifles)
YOC Young Officers Company
YS Young Soldier