Green’s Dictionary of Slang

weasel n.

1. (also weasle) a general derog. term; also as adj. [reverse anthropomorphism; Williams has 17C use of weasel, a lecher].

[UK]T. Killigrew Parson’s Wedding (1664) V iv: Who would choose such weazels as we see daily marry’d? that are all head and Tail, crooked, dirty, Sold Vermin, predestin’d for Cuckolds, painted Snails, with houses on their backs, and horns as big as Dutch cows; would any woman marry such?
[UK]J. Mills Old Eng. Gentleman (1847) 156: That polecat, Fiddylee, I saw to-day [...] the weasel couldn’t look me in the face.
[UK]E.V. Kenealy Goethe: a New Pantomime in Poetical Works 2 (1878) 336: Blusterer, Saucebox, Smell-feast, Weasel, / Swasher, Swaggerer, Princock, Chuff.
[US]Ade Girl Proposition 4: [He] saw her come out with the Human Weasel.
[UK]Bath Chron. 9 May 10/6: Mrs Braund [...] called Nellie Painter [...] a weasel; Nellie replied, ‘You need not be “ikey”; you’re only a barmaid’.
[US]M.G. Hayden ‘Terms Of Disparagement’ in DN IV:iii 197: weasel, a mean, greedy or sneaking fellow.
[UK]Marvel 17 July 7: I dunno, my poor little weasel-snouted idiot.
[US]K. Brush Young Man of Manhattan 111: Why, the weasel’s plastered!
[US]Kerouac letter 30 Mar. in Charters I (1995) 55: I hope Pop comes home [...] so that you’ll have the old weasel around to argue with.
[US]J. Blake letter 31 Mar. in Joint (1972) 115: Two-man cells being at a premium, it took a little maneuvering to keep out the hardnoses and weasels who figured to move in.
[US]Current Sl. IV:2 10: Weasel, n. An unattractive male.
[US]Eble Campus Sl. Apr. 4: weasle – a person who plays ends off against the middle [...] Lee only roots for whoever’s winning as usual. He’s being a weasle.
Superman II [film script] A lying weasel like you couldn’t resist the chance.
[US]H. Gould Double Bang 129: Little weasel greaseball.
[US]B. Hamper Rivethead (1992) 32: The man with the clipboard [...] just another weasel in a short-sleeve shirt, deputized to protect the status quo.
[Aus]L. Redhead Cherry Pie [ebook] ‘Bastard was good looking, especially compared to most of the other weasels on the scene’.

2. in attrib. use of sense 1.

[UK]G. Knight Hood Rat 108: A wiry kid [...] wading up the street with two lanky weasel mates on each shoulder.

3. (US) a native of South Carolina [the state has a large population of the animal].

[US]St Louis (MO) Reveille 14 May 2/4: The inhabitants of [...] South Carolina [are called] Weasels [DA].
[US]Montana Post (Virginia City, MT) 28 Apr. 4/1: The inhabitants of [...] South Carolina [are called] Weasels.
[US]Semi-Wkly Louisianan 31 Aug. 1/3: The Nicknames of the States [...] Rhode Island, gun flints; South Carolina, weasels; Tennessee, whelps; Texas, beefheads; Vermont, green mountain boys; Wisconsin, badgers.
[UK]Chambers’s Jrnl 13 Mar. 171/2: South Carolina is Palmetto State, and the natives are Weasels .
[US]Whitman ‘Sl. in America’ in North Amer. Rev. Nov. 433: Those from Maine were call’d Foxes; New Hampshire, Granite Boys; Massachusetts, Bay Staters [...] South Carolina, Weasels.
[UK]J. Ware Passing Eng. of the Victorian Era.

4. (US) an informer.

[US]H. Yenne ‘Prison Lingo’ in AS II:6 281: Weasel — Unpaid guard, usually an inmate that tells on another.
[US]G. Milburn ‘Convicts’ Jargon’ in AS VI:6 442: weasel, n. An informer.
[US]Monteleone Criminal Sl. (rev. edn).
[US]W. Brown Teen-Age Mafia 117: The guy knew what to expect if he turned weasel.
[US]C. Stroud Close Pursuit (1988) 139: Field Associate! What a name! Spy, snitch, stoolie, fink, rat, weasel — they were closer to the mark.

5. (orig. US) the penis [it ‘burrows’].

[US] in Randolph & Legman Ozark Folksongs and Folklore (1992) I 413: ‘A dollar gold for a piece of cock, / Pop! goes the weasel!’ [...] She learned it near Pineville, Missouri, before 1910.
[US]Randolph & Legman Ozark Folksongs and Folklore I 414: The chorus, Pop!, goes the weasel! has always been understood to refer to the ‘popping’ of the penis into the vagina [...] and only Eric Partridge, the world’s clumsiest amateur etymologist, can miss or overstate the point so fatuously, in his Shakespeare’s Bawdy (1948) p. 169, as to believe the Pop! is that of ejaculation.
[US]J. Lansdale Rumble Tumble 94: I’m not playing the horizontal tango with some redneck’s weasel, you look me up.

6. (US Und.) a private detective.

[US]Ersine Und. and Prison Sl.

7. (US) a pistol, a revolver.

H.B. Darrach Jr. ‘Sticktown Nocturne’ in Baltimore Sun (MD) 12 Aug. A-1/5: Pistol packin’ Mama [...] had never shipped a weasel, and didn’t know how she had come by her nickname.

8. (N.Z.) a sly or devious person.

[US]Goldin et al. DAUL 235/1: Weasel. 1. A crafty person without scruples.
[NZ]G. Newbold Big Huey 255: Weasel (n) Sly or devious person. In the sense of an informer, British, since the early 1930s.

In derivatives

weasel-assed (adj.)

a general derog. description.

[US](con. 1968) D.A. Dye Citadel (1989) 120: I was just trying to see that weasel-assed tank driver didn’t accidentally hit reverse.
weasely (adj.) (also weasily)

a general derog. description; image is of untrustworthiness.

[Aus]D. Maitland Breaking Out 281: I hardly think a pathetic weasily little bloody runt like you [...] could possess anything that would intimidate me.
[UK]W. Boyd ‘On the Yankee Station’ in On the Yankee Station (1982) 114: Weasely shit-face Lydecker.

In phrases

grease the weasel (v.)

(US teen) to have sexual intercourse.

Online Sl. Dict. [Internet] ‘greasing the weasel’ v. Sexual intercourse. If someone is ‘greasing the weasel’, it means that they are having sex. For example, ‘he’s not coming out coz he’s greasing the weasel with his misses.’ Dick equals weasel, greasing through sex.