Green’s Dictionary of Slang

1. (orig. US) carelessly, incompetently.

1934		(con. 1920s) J.T. Farrell Young Manhood in Studs Lonigan (1936) 337: If I plan to do something, I don’t see any reason to do it half ass.
1941		H. Steig Send Me Down 366: Even that you do half-assed.
1967		N. Mailer Why Are We in Vietnam? (1970) 133: Grizzer he eats awhile [...] and then works a little half ass at covering the carcass over.
1977		M. Herr Dispatches 54: The machine [was] running halfassed and depressed.
1985		D. Bodey F.N.G. 206: I sort of half-ass offer it to him.
1996		UGK ‘3 in the Mornin’ 🎵 I never understood what made you think you was handlin’ / You half-ass runnin’ through my neighborhood vandlin’.
1997		L. Pettiway Workin’ It 114: I was a C student. When a test came I half-ass cheated.
2001		Source Aug. 188: Don’t misinterpret this as Beans going half-ass in the studio or not caring if he makes music.
2011		G. Hayward Corruption Officer [ebk] cap. 6: Some just leaned against the wall half-ass listening to what was being said.
2018		R. O’Neill ‘Ocker’ in The Drover’s Wives (2019) 181: Never mind the woodpile coming a gutser. Bludger’d built it half arsed.

2. not seriously.

1964		Larner & Tefferteller Addict in the Street (1966) 78: I was using stuff but I wasn’t hooked; it was still half-ass.
1971		R. Woodley Dealer 149: ‘[S]hit, if I couldn’t be good, I wouldn’t do it. I sure as hell wouldn’t do it half-ass’.
1996		E. Bunker Dog Eat Dog 5: ‘I halfass wish I didn’t have this parole,’ he said.

3. reasonably.

1973		E. Bunker No Beast So Fierce 91: You used to be a halfass pretty kid. You won’t be able to catch yourself a man when you get back.
1985		N. Pileggi Wiseguy (2001) 50: The places were usually half-assed connected.
1996		E. Bunker Dog Eat Dog 9: She was a good broad. Halfass pretty, too, if she’d lose fifteen or twenty pounds.
2023		(con. 1962) J. Ellroy Enchanters 267: They wer half-assed good-looking [...] trim.