Green’s Dictionary of Slang

1. a dog, usu. a mongrel.

1902		C.L. Cullen More Ex-Tank Tales 16: The mutt [...] handed me a bunch of barks.
1919		in A. Cornebise Amaroc News (1981) 19 Oct. 116: There was lots of fun on the day the ‘Y’ was feeding chicken and all the bones were thrown under the table for the hungry bunch of mutts.
1928		J. Callahan Man’s Grim Justice in Hamilton Men of the Und. 278: I loved that mutt!
1931		(con. 1900s) C.W. Willemse Behind The Green Lights 127: The only dogs that have the right to the title are the mongrel mutts that hang around the police station.
1941		Lena Horne ‘The Captain and His Men’ 🎵 See that commander, how he struts, / Followed by the neighbors’ barking mutts.
1950		G. Marx letter 3 Oct. in Groucho Letters (1967) 193: He is an old cocker named Jo-Jo [...] The stupid mutt doesn’t know that it wouldn’t be in my room.
1960		G. Swarthout Where the Boys Are 187: One of the handlers [...] gestured at his mutt.
1971		B. Malamud Tenants (1972) 21: Harry grabbed the mutt, alternately whimpering and snarling, by a frayed rope collar.
1988		Beano Comic Library Special No. 12 41: I’ve put a cat flap in the door, just as you wanted, moggy. Thanks, mutt.
1993		K. Lette Foetal Attraction (1994) 124: And I’m not looking after that stupid mutt of yours either.
1998		K. Anderson Night Dogs 18: ‘What’s with the mutt?’.
2007		C. Goffard Snitch Jacket 17: It’s like trying to be friendly with an ugly, kicked-around dog [...] all the mutt does is show you its ass.
2010		K. Richards Life 530: The mangiest jet-black terrier [...] ‘He’s a hell of a mutt. Keith’.
2014		S. Grand ‘A Bottle of Scptch’ in ThugLit Mar. [ebook] Roxy — my mutt of unknown origin.

2. (also mut) a second-rate racehorse, i.e. a dog n.² (1)

1899–1900		C.L. Cullen Tales of the Ex-Tanks 81: The mut won’t be one, two, three.
1967		J. Schaefer Mavericks (1968) 63: We’ll run that jug-headed mutt of yours off its legs tomorrow.

3. (US, also mut) a fool, a bungler, an ignoramus; thus used as a general term of abuse, thus mutty, foolish.

1900		A.H. Lewis ‘Crime That Failed’ in Sandburrs 81: D’ old mut makes a straight wake for d’ priest.
1901		‘Hugh McHugh’ Down the Line 79: I knew Clara Jane would cancel the contract with the mutt [...] just as soon as she saw the automobile.
1911		G. Bronson-Howard Enemy to Society 211: Some of those fearless mutts who are ashamed to fight less than three at a time but start to ‘squeal’ the minute a copper taps them on the shoulder.
1922		A. Christie Secret Adversary (1955) 103: ‘I guess I’m a mutt,’ said Julius with unusual humility.
1924		C.J. Dennis ‘’Ave a ’Eart!’ in Rose of Spadgers 75: The rat-face mutt is dancin’ up an’ down.
1925		N. Lucas Autobiog. of a Thief 72: The police ain’t such muts [sic] as Sherlock Holmes liked to make out.
1930		(con. 1890) G. Milburn ‘A Convention Song’ in Hobo’s Hornbook 26: Each ’bo throwed his guts while the other mutts / Laid back and lent an ear.
1936		Queenslander (Brisbane) 2 July 4/4: Gone is thy glory with all its Rose, / Your ‘brush’ has skipped, wither gone who knows! / But still you think she’ll reappear? You mutt! / Be wise and say: ‘Bah, let her go.’ .
1937		A. Christie Murder in the Mews (1954) 35: Like the double-dyed mutt I must be, I couldn’t find anything.
1945		C. Mann ‘The Reader’ in River and Other Stories 35: You’re a mutt, Dowden.
1955		B. Appel Tough Guy [ebook] Christ [...] he’d show those mutts who was kissing jewboys.
1959		A. Sinclair Breaking of Bumbo (1961) 157: Don’t be a mutt.
1960		J. Havoc Early Havoc 220: ‘Poor little mutt — got yourself married’.
1975		E. Torres Carlito’s Way 101: He came to Rocco’s house with Earl and with this mutt Carlito.
1987		T. Wolfe Bonfire of the Vanities 6: He’s the mayor of White New York! Set fire to the mutt!
1992		R. Price Clockers 396: There were four mutts in the holding cell.
1999		Observer Rev. 27 June 6: The librarian (a swot and a mutt combined).
2005		K. Huff A Steady Rain I i: We kinna adopted the mutt. Heinz took a shine to him.
2016		D. Whish-Wilson Old Scores [ebook] The mutts in the front seats were too drug-fucked to recognise him.
2017		D. Winslow The Force [ebook] You feel for the old lady victim, but hate the mutt who did it.
2020		D. Whish-Wilson Shore Leave 201: ‘I don’t keep the same company I used to. No interest in a mutt like him’.

4. any animal.

1906

S. Ford Shorty McCabe 125: The poor old mutt [i.e. an elephant] had quit after a few jumps.

5. used affectionately.

1934

M. Fulcher ‘Believe Me’ in Afro-American (Baltimore, MD) 29 Dec. 12/2: After all, he is a right good old mutt.

6. an unattractive person of the opposite sex.

1987		G.A. Fine With the Boys 169: Mutt, n. Disliked or ugly girl.
1991		R.G. Barrett Between the Devlin 54: ‘Better than those cheesy old mutts you drag through the door’.
2004		P. Howard PS, I Scored the Bridesmaids 23: I’m like, Go and take the dogs for a walk, because in fairness they are all mutts.