Green’s Dictionary of Slang

1. a sailor.

1854		Swell Life at Sea 21: While a man-of-war comes in at one end, we can slip out at the other. If this does not prove that Jemmy Flatfoot had a hand in laying out the coast of Africa, yon [sic] may call me a marine.
1891		’Sailors’ Lingo’ in Hants. Teleg. 21 Feb. 11/3: Jack is addressed as a ‘matelow’ or ’flat foot’.
1899–1900		C.L. Cullen Tales of the Ex-Tanks 371: My fo’c’sle shipmates were all old flat-feet.
1904		Kipling ‘The Bonds of Discipline’ in Traffics and Discoveries 53: Any flat-foot who presumed to exhibit surprise [...] would be slightly but firmly reproached.
1912		N.Z. Colonist 12 Dec. 2/5: The sailor-man is a ‘Matloe’ or ‘Flatfoot’.
1918		‘Commander’ Clear the Decks! 59: When little shin-digs of seamanship like a foul anchor or propeller are amusin’ to flat-feet (bluejackets) no one lends a hand to yours truly.
1925		(con. WWI) Fraser & Gibbons Soldier and Sailor Words 95: Flat Foot, A: A sailor.
1930		(con. 1910s) L. Nason A Corporal Once 114: ‘You ain’t there yet,’ said the flatfoot. ‘To-morrow we get into the submarine zone.’.
1944		P. Kendall Dict. Service Sl. n.p.: a flatfoot . . . a sailor.

2. an infantryman; also infantry in attrib. uses.

1862		letter q. in Wiley Life of Johnny Reb (1943) 342: I wood rather be a corporal in company F of the Texas Rangers tha to be the first Lieu in a flafoot company.
1864, 1867, 1870		Hotten Sl. Dict.
1873		Sl. Dict.
1889–90		Barrère & Leland Dict. of Sl., Jargon and Cant.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1918		‘Sapper’ Human Touch 244: Two frapping turns, you perishing flat-foot.
1943		(con. 1860s) B.I. Wiley Life of Johnny Reb 342: I wood rather be corporal in company F of the Texas Rangers than to be first Lieu in a flat foot company.

3. (also flat, flat heel) a police officer, a (private) detective.

1885		Bulletin (Sydney) 25 Apr. 10/3: Where is the glamour of golden youth? / Where are the joys of jeunesse dorée? / When a flat-foot man, with a build uncouth, / With a thick-set brogue and a bearded tooth, / Can run you in – Gadzooks! Forsooth!].
1895		J. Caminada Twenty-Five Years of Detective Life I 34: ‘What a lot of flats you have brought with you’ (flats being the thieves’ term for policemen in uniform).
1901		W.S. Walker In the Blood 162: There’s Chinke’s drums chock full o’ young girls, an’ the ‘flat-foot’s’ ’aven’t ’arf a chanst to get in there.
1906		O.C. Malvery Soul Market 290: A policeman in uniform is a ‘flat’.
1914		Sport (Adelaide) 27 Mar. 3/2: A B, [...] had better mind or he will be charged by PC Flatfoot for kidnapping .
1915		S. Ford Torchy, Private Sec. 152: Only one of them cheap flat-foots. Don’t mind him.
1916		J. Lait ‘Canada Kid’ in Beef, Iron and Wine (1917) 162: It’s a dirty shame after I done swell lifts for years and bulled the swellest bulls outta the Chief’s office, to get picked up by a flatfoot in harness.
1924		G. Henderson Keys to Crookdom 346: The policeman, patrolman or ‘flatfoot’ rarely comes in contact with a criminal, unless he happens to find one committing a felony on his beat.
1932		(con. 1910s) J.T. Farrell Young Lonigan in Studs Lonigan (1936) 73: He [...] stepped up to the lousy flatfoot.
1934		B. Traven Death Ship 23: The two flats were armed.
1938		L. Ortzen Down Donkey Row 25: The splits say we’re a menace – not the flat-feet from the station round the Johnny Horner.
1939		R. Chandler ‘Trouble Is My Business’ in Spanish Blood (1946) 199: I’m just a dumb flatheel.
1941		A. Gurney Bluey & Curley 30 June [synd. cartoon strip] You lop-eared flat-foot!!
1946		Mezzrow & Wolfe Really the Blues 131: Looking over our shoulders to see if that flatfoot was trailing us.
1955		Mad mag. July 35: [...] a regular Chauncey Depew in flatfoot’s guise.
1959		E. De Roo Go, Man, Go! 146: Those flat-feet couldn’t find their shoes.
1959		J. Gosling Ghost Squad 151: I’ve known you since you were a flat-foot, John [...] but I won’t help you.
1964		H. Selby Jr Last Exit to Brooklyn 166: fuck you flatfoot go and fuckyaself yasonofabitch.
1976		Cab Calloway Of Minnie the Moocher and Me 10: From the precinct captain to the flatfoot on the beat.
1982		S. King Running Man in Bachman Books (1995) 578: He was going to be some dumb flatfoot’s fluke trophy.
1987		W.T. Vollmann You Bright and Risen Angels (1988) 313: Then we get the flatfeet to clear the book on them.
1996		J. Cameron It Was An Accident 67: Not your regular flatfoot. Type they brought out for meeting the queen. Chief Superintendent.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 70/2: flatfoot n. a police officer.
2003		M.A. Collins Dick Tracy 5: A master at the detective story [...] writing the world’s most famous flatfoot.
2012		(con. 1980s) I. Welsh Skagboys 395: The rash ay warehouses, cobbled streets and tenemented dwellings adores its sons and hates auld flatfoot who’s brought nowt but grief doon here since the year dot.

4. attrib. use of sense 3.

1940		S. McBarron ‘Coffin Custodian’ Ten Detective Aces Apr. 🌐 I was remembering something the instructor at Flatfoot School teaches all his little rookies.
2010		J. Ellroy Hilliker Curse 14: Private fuzz ran pricey. A flatfoot fleet safeguarded me.

5. (US) a man who stands firmly for one political party, come what may.

1887

R.A. Proctor ‘Americanism’ in Knowledge 1 June 184/1: An American ‘flatfoot’ is a man who stands firmly for his party.

6. a person who has flat feet.

1922

Joyce Ulysses 375: Some flatfoot tramp on it in the morning.

7. (US) a fool.

1922

T. Thursday ‘Ten Dollars – No Sense’ in Top-Notch 15 Dec. 🌐 Call for assistance, you poor flatfoot.

8. (US) an Irish immigrant.

1968

in DARE.