Green’s Dictionary of Slang

1. to hit in the face, to give someone a black eye; thus mousing n. [note SE mouse, to handle roughly, as a cat does a mouse].

1678		Dryden Kind Keeper III i: Your kept Mistress is orignally a Punk; and let the Cat be chang’d into a Lady never so formally, she still retains her natural property of Mousing.
1842		Wkly Rake (NY) 3 Sept. n.p.: If he ain’t a darned Yankee, right up to snuff; / At playing on tater traps — touching a lug — / At mousing a peeper — or spoiling a mug .
1867		Nat. Police Gaz. (NY) 16 Nov. 2/2: ‘You shut, or I’ll mouse you tomorrow’.
1874		Leeds Times 28 Mar. 6/5: A young man with a frightfully contused optic [...] ‘Who’s bin a mousin’ on yer, old man?’.

2. to engage in sexual activity (usu. short of intercourse).

1732		Progress of a Rake 18: Wives and Servants, Girls and Daughters, / Must keep a Padlock on their Quarters; / If Dick came in the way to mouze ’em.
1839		Crim.-Con. Gaz. 25 May 137/1: I saw old Weston [...] billing and cooing with some of his customer’s wives [...] really, old chap, it is now high time to give over your mousing propensities.
1928		Hecht & MacArthur Front Page Act III: Mousing around with some big blond Annie!
1942		Berrey & Van den Bark Amer. Thes. Sl.
1956		H. Gold Man Who Was Not With It (1965) 296: Hit me! hit me! You’ve been mousing Nancy’s wife!
1966		Current Sl. I:1 5/2: Mouse To kiss.
1973		G. Swarthout Luck and Pluck 78: ‘Now let’s mouse.’ She [...] put one arm around him and one hand at the back of his head and kissed him.
1986		R. Ford Sportswriter 76: A whole lot of us would like to mouse off with a little nurse.
1999		D. Lypchuk ‘A dirty little story’ in eye mag. 8 July 🌐 He boxed her tonsils and she moused him back. She was getting all beady and soppy.

3. (Aus.) to perform any action quietly.

1895

C. Crowe Aus. Sl. Dict. 50: Mouse, be quite; talk low; softly step, etc.

4. (US Und.) to inform on.

1950		Goldin et al. DAUL 142/1: Mouse, v. To inform against associates.
1956		N. Algren Walk on the Wild Side 145: He’ll mouse on me and he’ll mouse on you [...] He’s a forty-faced pigeon straight from Rat Row, quack from head to toe.
1967		R. Starnes Requiem in Utopia 182: That’s two guys who might someday come to be bad friends with you, and mouse.

5. (US) to blackmail; thus the mouse n., extortion [note 19C US mouse, to poke about].

1972		B. Rodgers Queens’ Vernacular 138: mouse [...] 2. (criminal sl) to blackmail a homosexual.
1986–7		Maledicta IX 144: Such terms as rent are not heard in the U. S., nor are the words for […] to mouse (perhaps a minor version of to rat, in any case meaning blackmail).