Green’s Dictionary of Slang

a bribe to ensure one’s silence, ‘hush-money’.

1821

in Egan Life in London (1869) 179: His law expenses and ‘mum tip1’ in consequence, were frightful. [1 note] ‘Silence!’ How extremely polite and gentlemanly to inform an individual that he will be ‘wanted’ on such a particular day, instead of dragging him away from his business and family, and locking him up like a felon; beside making a buz about his premises, which not only knocks up his credit in the neighbourhood, but spoils his reputation at a distance. Why such accommodation is worth any tip.

to keep quiet; thus 1940s exhortation to secrecy, be like Dad, keep Mum.

1839		T. Haliburton Clockmaker 14: Four sovereigns more, massa, and steward he keep mum, and if you no pay de money, I go bring captain, passenger and ebery one.
1848		‘Ned Buntline’ Mysteries and Miseries of N.Y. III 47: If he had lost seven thousand instead of hundreds he would have kept mum about it. [Ibid.] IV 28: I’ll keep as mum as a mouse when the cat’s about!
c.1858		J.H. Green Secret Band of Brothers 31: ‘Mind, Green, what I have said. Keep mum, and I will have them back at the risk of —’ She was interrupted by the landlady, who very kindly assisted her in finishing her sentence by adding — ‘at the risk of perjuring yourself!’.
1867		‘Artemus Ward’ Artemus Ward in London in Complete Works (1922) 491: Keep mum [...] I only wanted to have some fun with them folks above us. I swar.
1873		W.H. Thomes Bushrangers 73: ‘Hush! don’t mention such a thing,’ was the reply. ‘We are not yet clear of the Mud-Laners. Keep mum; all will be well.’.
1884		(con. c.1840) ‘Mark Twain’ Huckleberry Finn 69: People would call me a lowdown Abolitionist and despise me for keeping mum.
1890		Queenslander 16 Aug. 298/3: I need not tell you to keep mum about the dish.
1898		(con. 1875) F.T. Bullen Cruise of the ‘Cachalot’ 168: I was getting pretty well versed in the tricks of the trade now, so I kept mum.
1907		C. M’Govern By Bolo and Krag 36: I would keep mum about having been ashore in a cholera town.
1907		Lone Hand (Sydney) June 174/1: Give me a man [...] / That’ll shut his napper and keep dead mum.
1914		C. Holme Lonely Plough (1931) 110: You’ve got to grit your teeth on your tongue to keep it mum.
1926		Boys’ Realm 16 Jan. 264: You keep mum about it [...] and I’ll explain later.
1930		G. Milburn ‘Who Said I Was a Bum?’ in Hobo’s Hornbook 145: I’ll tell you who I really am, / I hope you’ll keep it mum – / I know I’m a hobo, but / Who said I was a bum?
1942		J. MacLaren-Ross ‘I Had to Go Sick’ in Memoirs of the Forties (1984) 255: ‘Don’t go opening your trap, see? Keep mum and don’t say nothing.’.
1951		D. Stivens Jimmy Brockett 189: I kept mum and waited.
1960		Mad mag. June 49: So I sat, and thought, and wrestled, keeping mum and feeling hassled.
1978		(con. 1940s) J.G. Farrell Singapore Grip 423: Maybe I’ve been speaking out of turn, maybe I should have kept mum about it.
1989		S. Armitage ‘Team Lada’ in Zoom 71: Racing home to burnt suppers; late, but with / a bouquet of excuses, keeping mum / about pit stops in the Coach and Horses.
1998		I. Welsh Filth 325: Just keep mum my darling, and I’ll be round to see you soon.
2005		E. Weiner Big Boat to Bye-Bye 34: I kept mum about the shirttail and introduced myself.
2011		Sun. Times News Review 6 Feb. 12/3: For pity’s sake, do keep mum.

be quiet, say nothing about this.

1670		Memoires of Monsieur Du Vall 12: After he had hang’d a convinient time, he was cut down [...] and so conveyed to the Tangier Tavern in St. Gile’s where he lay in State [...] Mum was the word, great silence expected from all that visited.
1700		T. Brown Amusements Serious and Comical in Works (1744) III 122: But Mum’s the Word — for who wou’d speak their Mind among Tarrs and commissioners.
c.1712		R. Estcourt Prunella 6: Hold your Tongue, Mun, Mum’s the Word.
1740		R. North Examen 126: So, Mum was the Word.
1796		J.G. Holman Abroad and At Home III ii: You know, one should not brag of one’s connexions, so mum’s the word before my father.
1809		B.H. Malkin (trans.) Adventures of Gil Blas (1822) I 247: I will not say a word about the run-away trick: that would render you suspected of turning nose; therefore mum is the word.
1821–6		‘Bill Truck’ Man o’ War’s Man (1843) 405: Recollect [...] that mum is the word on your part.
1837		‘The Two Butlers’ Bentley’s Misc. Mar. 311: Well, then, mum’s the word.
1846		Durivage & Burnham Stray Subjects (1848) 90: Look there! – mum’s the word, you know.
1851		G. Thompson Jack Harold 62: Mum’s the word, captain.
1862		Thackeray Adventures of Philip (1899) 421: Mum’s the word!
1870		Old Hunks in Darkey Drama 5 47: Mum’s the word!
1885		Bulletin (Sydney) 28 Feb. 12/2: ‘Mum’s the word. All friends here. […] A-jew!’.
1887		J. Payn Glow-Worm Tales III 49: ‘Mum is the word,’ observed the page, and he winked.
1893		P.H. Emerson Signor Lippo 66: Now I knew the game. But ‘mum’s’ the word, I said to myself.
1893		K. Mackay Out Back 125: ‘Mum’s the word, then,’ said Jim.
1900		C. Chesnutt House Behind The Cedars (1995) 110: But mum’s the word! If I hear a whisper of this from any other source, out you go, neck and crop!
c.1900		Mills & Scott [perf. Marie Lloyd] You needn’t wink, I know! 🎵 You needn’t wink, old chap,- mum’s the word — I know!
1906		Sun. Times (Perth) 23 Dec. 1/1: The girlie complained [and] the Yellow Agony immediately proffered the parents a tenner as mum’s-the-word jmoney.
1910		Marvel 15 Oct. 5: ‘S’sh!’ he murmured. ‘Mum’s the word!’.
1920		‘Sapper’ Bulldog Drummond 70: Above all, James — mum’s the word.
1922		Joyce Ulysses 145: Does himself well. No guests. All for number one. Watching his water. Bring your own bread and butter. His reverence. Mum’s the word.
1934		J. Franklyn This Gutter Life 103: ‘Mum’s the bloody word.’ ‘Quite,’ answered Gerrard.
1945		G. Fairlie Capt. Bulldog Drummond 24: In the meantime I think it better be mums the word.
1959		I. & P. Opie Lore and Lang. of Schoolchildren (1977) 161: When wishing a person to keep a thing quiet children ordinarily enjoin ‘Keep it dark’ [...] ‘Mum’s the word’.
1960		‘Hergé’ Tintin and the Red Sea Sharks 10: ‘Mum’s the word,’ that’s our motto.
1976		J. Heller Good As Gold (1979) 342: Mum’s the word, right?
1985		A. Payne ‘Minder on the Orient Express’ Minder [TV script] 116: Yeah, okay. Mum’s the word.
1993		Tarantino & Avery Pulp Fiction [film script] 65: Mum’s the word.
2001		(con. 1964–8) J. Ellroy Cold Six Thousand 267: Mum’s the word. A good reporter doesn’t reveal his sources.
2015		S. King Finders Keepers (2016) 253: ‘If you tell the Barbster, I’ll never hear the end of it.’ ‘Mum’s the word’.
2021		J. Ellroy Widespread Panic 168: ‘Don’t tell me too much, baby.’ ‘You’re right. Mum’s the word’.
2024		J. Meades Empty Wigs (t/s) 658: I knew a thing or two about being sullied but it wasn’t a competition so mum’s the word.