Green’s Dictionary of Slang

1. a self-serving braggart and cheat; thus trimming adj., boastful.

1567		Trial of Treasure Ciii: O maister Luste, she hath an amiable face, A tricker, a trimmer, in faith that she is.
c.1680		E. Hickeringill The Trimmer’s Debate with the Observator in Works (1709) I 357: I am against all Peace with Whigs, Trimmers, or Dissenters and am only for Execution.
1708		True Characters of A Deceitful Petty-Fogger et al. 13: A Trimmer, or Jack of all Sides, Is a Will with a Whisp, a Man of no Principle, either of Honour or Conscience, any further than it squares with his Safety and Profit. [Ibid.] 15: If our Trimming Whig is a Man of Authority, he will Ruin you with Trust and Confidences.

2. a thing that defeats another, e.g. a blow, a stiff letter etc.

1768		Foote Devil Upon Two Sticks in Works (1799) II 261: A trimmer. This will make some folks that we know look about them [...] this will sting.
1770		T. Chatterton Revenge I vi: Aha! —bring me a stick here — / I’ll give you a trimmer, / You bladder of air —.
1816		W. Scott Antiquary in Waverley (1855) II 67: I will show you his last epistle, and the scroll of my answer – egad, it’s a trimmer!
1894		C.H. Hoyt A Milk White Flag Act II: Yes, you old geezer! You coffin trimmer!

3. a person who beats, scolds, reprimands etc.

1823		[C.M. Westmacott] Mammon in London 1 224: My charming Anne was a trimmer — a limb of the devil — and had already made the house too hot to hold me.
1827		Sporting Mag. XXI 141: Amongst the young hounds I noticed some trimmers .
1888		W.B. Churchward Blackbirding In The South Pacific 44: You have killed the best blackbirder in the whole Pacific. He was a trimmer, he was, and no mistake. He never spoke twice to any man. I was his mate once, when he gouged this eye out, because I wanted to go on shore.
1934		T. Wood Cobbers 19: He was a trimmer, rough as bags, and rich as you like. Friends with everybody though.
1937		A.W. Upfield Murder Down Under (1951) 53: Mrs Wallace was the triumphant victor holding the fort. ‘She’s a trimmer,’ announced the Spirit of Australia, chuckling dryly.

4. a thieving prostitute.

1931

(con. 1900s) C.W. Willemse Behind The Green Lights 70: He barred from the Haymarket every girl who ever had been arrested for theft or who was known as a ‘Trimmer.’.

5. (US Und.) a swindler; a confidence trickster; also a crooked lawyer.

1891		S.M. Welch Recollections of Buffalo 1830-40 293: There was an esprit de corps of reliability and honor in their practice; excluding such characters as are known as ‘Shysters,’ ‘Tombs Lawyers,’ ‘Trimmers,’ and lawyers guilty of ‘sharp practice.’.
1900		Sporting Times 17 Feb. 1/2: The trimmer or traitor who dares to cray ‘Halt,’ / You can leave to the man in the street.
1923		O.O. McIntyre New York Day by Day 14 Sept. [synd. col.] The bucketeers [...] found trimmers could be trimmed by the baby smiles of ruby-lipped charmers.
1940		H. Drake-Brockman Hot Gold I i: It’s that Rienzi. He’s a trimmer. Always laring round.
1949		Monteleone Criminal Sl. (rev. edn).

6. (US) a dice cheat.

1902

Nat. Police Gaz. (NY) 27 Dec. 6/1: The sporting fraternity is partial to craps, because you get action for your money all the time, except when the ‘trimmers’ work a pair of ‘phonies’ on you. Then the ‘trimmer’ gets the action all to himself, if you don’t ‘get wise.’.

7. (N.Z.) a spoilsport, a disappointment.

2006

P. Shannon Davey Darling 199: You are a bloody trimmer, Davey. I go to all this trouble of making sure you get your vegetables and you just don’t seem to care.