The following comprises a list of words and phrases of the Armed Forces of the United Kingdom of Great Britain during the Great War, which also includes slang of the trenches and the Air Force; British and American service terms and expressions in everyday use; nicknames, sobriquets, and the titles of British and Commonwealth Regiments and their origins; and warfare in general. These words and phrases are contemporary to the war, which is reflected in the style and language used of the time, some of which may seem derogatory by today's standards. The following words and phrases have been transcribed from three primary sources (see contents). Feel free to help improve any of the entries in these lists.
- FA
- Fag issue
- Fairy light
- Fan tan
- Fancies, The
- Fancy religion, The
- Fanny Adams
- Fannys, The
- Fashy
- Fatigue duty
- Fatted for the slaughter, Being
- Feather, The
- Fed up
- Feel out
- Felix
- Female tank
- Fernleaves
- Fetch up
- FIDAC
- Fiddler
- Fiddler's Green
- Field Army
- Field Marshal (rank)
- Field rats
- Finee
- Finger and thumb (rhyming slang)
- Fireworks
- First of the moon
- First post
- Five pence halfpenny
- Fix, At the word
- Fixed bayonets
- Flag of Truce
- Flag-wagging
- Flaming onions
- Flanders
- Flank
- Flanker
- Flap
- Flapper's delight
- Flat foot
- Flattening out
- Flesher
- Flight
- Flimp
- Flip
- Floaters
- Floating L's
- Flog
- Florin
- Florrie Ford
- Fluff
- Fly boys
- Fly-catchers
- Fly slicer
- Flying bedstead
- Flying kite
- Flying matinée
- Flying pig
- Fokker
- Follies, The
- Follow the band
- Follow the drum
- Football
- Footslogger
- For it
- For the duration
- Force D
- Foreign Legion
- Forking the beam
- Four bag
- Four by two
- Four-flusher
- Forlorn hope
- Fourth Army
- Fragmentation (weaponry)
- Franc
- Franc-tireurs
- Frangine
- Fred Karno's Army
- Fred Karno's Navy
- Free gangway
- Free tank
- Friday while
- Friendly, A
- Frightfulness
- Frigo
- Frog and toad
- Frogging it
- Fritz
- Front
- Frontier
- Frying pans
- Full con
- Full pack
- Function, To
- Funk-hole
- Funky villas
- Furious joy
- Furphy
- Furphy King
- Fusilier