- 9 March
- 9 May
- 9 November
- 9 October
- 9 September
- ADC
- AD Corps
- AEC
- AEF
- AO
- AOC
- AP
- APC
- APM
- ASC
- AVC
- A baralong fate
- A do
- A fancy religion
- A friendly
- Abbeville
- Abdominal crash
- Abdul
- Abercorn (Rhodesia)
- Ablain (Vimy)
- About the Great War 'on this day'
- About turn
- Achi Baba (Gallipoli)
- Ack
- Ack Emma
- Acting rabbit pie
- Ada Tsiganlia
- Adam and Eve
- Adam and Eve (rhyming slang)
- Adam and Eve on a raft
- Adam and Eve wrecked
- Addressed to
- Aden
- Adige (river)
- Adjutant
- Adjutant (rank)
- Admiral (rank)
- Admiral Troubridge
- Admiralty
- Admiralty ham
- Admiralty to all ships
- Adolf Ahlers
- Adriatic
- Adrift
- Aegean Sea
- Aeroplane
- Aerschot
- Aerschot (Belgium)
- Africa
- Afters
- Aggie
- Ah wee
- Ahwaz (South-West Persia)
- Aide-de-camp
- Air pills
- Air raid
- Air torpedo
- Aire (river)
- Airship
- Aisne
- Aisne-Marne Canal
- Aisne (river)
- Aivali (North of Smyrna)
- Ak Dum
- Akaba (North Red Sea)
- Alashgerd (Armenia)
- Albania
- Albert (Somme)
- Albert I of Belgium
- Alchi Tepe (Dardanelles)
- Alexander Samsonov
- Alexandre Millerand
- Alexandretta
- Alice
- Alien
- All arms and legs
- All callio
- All cando
- All cut
- All highest
- All kiff
- All of a doodah
- All out
- All over oneself
- All spruced up
- Allenstein
- Alley
- Alley at the toot
- Alleyed
- Alleyman
- Allied
- Allies
- Allumettes
- Alsace
- Altkirch
- Altkirch (Alsace)
- Amara (Mesopotamia)
- America
- Amiens
- Ammo
- Ammos
- An 'alf a mo
- An agony
- An air flapper
- An angel
- An egg
- Anafarta (Gallipoli)
- Anatolia
- Ancona (Northern Italy)
- Andrew, The
- Andrew Bonar Law
- Angel's whisper
- Angel face
- Angels of Mons
- Angola
- Angry cat
- Annie's room
- Ante-up
- Anticks
- Antivari (Montenegro)
- Antonio
- Antwerp
- Antwerp expresses
- Anty
- Any more for any more?
- Anzac
- Anzac Cove
- Apples and pears (rhyming slang)
- Apree la Gare
- Apremont (Argonne)
- Archduke Franz Ferdinand of Austria
- Archie
- Archie (Archibald)
- Archie barrage
- Ardahan
- Area shoot
- Argonne
- Ari Burnu (Gallipoli)
- Armadillo scout
- Armentieres
- Armentières
- Arminteers
- Armistice
- Armstrong hut
- Army
- Army Council
- Army Service Corps
- Arras
- Arrival
- Arsiero (Trentino)
- Artillery
- Artois
- Artvin (Armenia)
- As many faces as a churchyard clock
- As you were
- Ash can
- Asia Minor
- Asiatic Annie
- Asiatic and Egyptian theatres
- Askaris
- Asquiths
- Astico (river)
- At the word, fix
- Atakpame
- Atkins
- Attaboy
- Attack in detail
- Auberive (Champagne)
- Aubers
- Aubers Ridge (Neuve Chapelle)
- Augustovo
- Augustovo (North Poland)
- Aus
- Aus (south-west Africa)
- Australia
- Austria
- Austria-Hungary
- Authuille
- Authuille Wood
- Avec
- Avlona (Albania)
- BAA Lamb
- BAB
- BB's
- BE
- BF
- BIO
- BL
- Babbler
- Baby
- Baby's head
- Baby Killers
- Baby crying
- Baby monitors
- Back-chat
- Backwash
- Baden
- Badgy
- Bag of
- Bag of rations
- Bagatelle
- Bagatelle (Argonne)
- Baggies
- Bagonet
- Bailleul
- Bakalaryevo
- Bake
- Balb
- Baligrod
- Baligrod (Carpathians)
- Ball and bat (rhyming slang)
- Ball of lead (rhyming slang)
- Balloo
- Balloon
- Band party
- Bandagehem
- Bandook
- Bandstand
- Bangalore torpedo
- Banjo
- Barber's Cat
- Barishnya
- Barker
- Baron
- Barrage
- Bartfeld
- Base Wallah
- Base of Operations
- Bashi-Bazook
- Basra
- Bassano
- Bat
- Bat Boat
- Batchy
- Bath Mats
- Batman
- Batoum
- Bats in the Belfry
- Battalion
- Battery
- Battery (artillery)
- Battle-Bag
- Battle-Bowler
- Battle of Coronel
- Battle surplus
- Battling L's
- Bay of Akbachi Sliman (Gallipoli)
- Bayazid
- Bayonet
- Bayonet trench
- Bazaar Motor Vans
- Beachy Bill
- Beaucoup
- Beauséjour
- Beauzec
- Beer
- Beetle-Off
- Being fatted for the slaughter
- Belgeek
- Belgium
- Belgrade
- Belgrade (Serbia)
- Bellied
- Belligerents
- Belly Band
- Belly flopping
- Bender
- Bernhard von Bülow
- Bert
- Beskid Pass
- Beskid Pass (Carpathians)
- Bethmann-Hollweg
- Bevvy
- Biff
- Big Bertha
- Big Willie
- Big boys
- Big noise
- Big stuff
- Bilge
- Bill Harris
- Bill Jim
- Billet
- Billy Wells
- Binge
- Bint
- Bird
- Birdcage
- Birdseed
- Biscuits
- Bismarck Archipelago
- Bivouac
- Bivvy
- Bivvy sheet
- Black Cow
- Black Maria
- Black Watch
- Black hand gang
- Blamont (Lorraine)
- Blank-ed
- Blankets
- Bleat
- Blighty
- Blighty bag
- Blighty one
- Blighty wound
- Blimp
- Blind
- Blind-O
- Blink
- Blinking
- Blip
- Blister
- Blob
- Block
- Blockade
- Blood
- Blood boat
- Blood money
- Blood on the bullet
- Bloody
- Bloody flag
- Blotto
- Blow
- Blow in
- Blow off the line
- Blue-eyed boy
- Blue-lights
- Blue Cross (chemical warfare)
- Blues
- Boa constrictor
- Bob-a-day gunner
- Bob-down man
- Bob tack
- Bobbajee
- Bobber
- Bobbery
- Bobbing drill
- Bobbing on
- Bobby's job