Green’s Dictionary of Slang

1. (UK Und.) a groat, four pence; in cit. 1798, fourpenny-worth [? f. MLG vleger, ‘a coin worth somewhat more than a Bremer groat’].

c.1566		Harman Caveat for Common Cursetours in Viles & Furnivall (1907) 83: flagg, a groate.
1592		Groundworke of Conny-catching [as cit. c.1566].
1608		Dekker Belman of London (3rd) H1: upr.: Why? Hast thou any lowre in thy bung to bowse? rog.: But a flag, a win, and a make.
1612		Dekker O per se O M4: There was another excellent Ben-feaker [...] who tooke two shillings and fiue pence (two Bordes and fiue Winnes,) or two Bordes and a Flagge for euery Passeport that went out of his beggarly Office.
1639		J. Taylor Crabtree Lectures 189: Cove. Mort, what lower hast thou in thy Bung? Cove. [sic] I have a boord, two flagges, a Make, and one jon, and a rum stocke too.
1648		Dekker Canters Dict. Eng. Villainies (9th edn).
1665		Head Eng. Rogue I 49: Flag, A Groat.
1674		Head Canting Academy (2nd edn).
1688		R. Holme Academy of Armory Ch. iii item 68c: Canting Terms used by Beggars, Vagabonds, Cheaters, Cripples and Bedlams. [...] Flagg, a Groat.
c.1698		B.E. Dict. Canting Crew n.p.: Flagg, c. a Groat.
1703		Hell Upon Earth 5: Flag, a Groat.
1714		A. Smith Lives of Most Noted Highway-men, etc. I 209: He taught his Pupil a deal of canting Words, telling him [...] Flag, a Groat.
1728		Defoe Street Robberies Considered 32: Flag, a Groat.
1741		Canting Academy, or the Pedlar’s-French Dict. 113: A Groat A Flag.
1754		Scoundrel’s Dict. 14: A Groat – Flag.
1789		G. Parker Life’s Painter 142: I say, my kiddies, there’s two bobsticks of slim, and a flag’s worth of lightening to pay.
1798		‘St Giles’s Greek’ in Sporting Mag. Dec. XIII 164/1: The cull [...] remained at the bowsing ken, cocking his organ, and tempering his fogus with a few flagges of crank and white-tape.
1811		Lex. Balatronicum.
1833		‘Knowing Bill’ in Rake’s Budget in Spedding & Watt (eds) Bawdy Songbooks (2011) III 86: Salt cod I sell a vind a pound, / Red herrings twelve a flag.
1835		G. Kent Modern Flash Dict.
1840		Flash Mirror 4: Fat Jack’s [...] where all path shavers are allowed to doss for a duce, gaff men for thrums, skin sneakers for a flag.
1857		‘Ducange Anglicus’ Vulgar Tongue.
1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor I 251/1: Bought for a ‘flag’ (fourpence).
1873		Sl. Dict.
1881		Morn. Bulletin (Rockhampton, Qld) 18 July 2/6: For fourpenny pieces we find the name of ‘bit,’ ‘castle-rag,’ ‘flag. [...] ‘joey,’ and ‘quarterer saltee’.

2. (US) a $1 note [var. on sense 1 or abbr. Jewish flag under Jewish adj.].

1930		J. Huston Frankie and Johnny 47: One flag an’ six singles—an’ the rest is silver [HDAS].
1944		in C. Himes ‘Let Me at the Enemy’ Coll. Stories (1990) 38: He keep right on an’ pick ’nother ton. Make forty flags.

3. (Aus.) a £1 note.

1925		Sun (Sydney) 3 Dec. 19/2: [headline] Wife’s Flag! She waved pound notes out of husband’s pocket.
1941		Baker Popular Dict. Aus. Sl.
1950		S.J. Baker in Sun. Herald (Sydney) 8 June 9/3: The underworld has an extensive vocabulary of financial terms. Among those recorded by Detective Doyle are: [...] ‘half a flag,’ ten shillings; ‘flag,’ ‘slice,’ ‘fiddley,’ and ‘oner,’ £1.
1952		Argus (Melbourne) 13 June 4s/3: 2 half-quids = 1 quid or flag.

4. (UK Und.) a cheque.

1935

Thieves Slang ms list from District Police Training Centre, Ryton-on-Dunsmore, Warwicks 4: Flag: Cheque.