Green’s Dictionary of Slang

see separate entries.

1. (mainly US) skewed, incorrect, out of one’s depth; socially inept.

1923		Proc. Aus. Law Institute I 180: If it does not imply it, aren't we a little off base in our theory.
1927		B. Cormack Racket Act I: Listen! You get off base with Joe Scarsi and you’ll get tagged out, like the last one who tried to take one of Nick’s friends for a ride.
1943		W. Brandon ‘Its so Peaceful in the Country’ in Ruhm Hard-Boiled Detective (1977) 322: I see I’ve got a little off base.
1955		Q. Reynolds Police Headquarters (1956) 166: Maybe we were off base. I don’t know. You’re a right footer, Frankie.
1969		J. Crumley One to Count Cadence (1987) 88: Sir, I know I’m off base, but the events of this morning seem to call for unusual actions.
1975		H. Ellison Deadly Streets (1983) 14: I must have been way off-base.
1976		E. Thompson Caldo Largo (1980) 80: OK. Just don’t bust a gut. I don’t give a fart if your taste in putas is off base.
1992		D. Burke Street Talk 2 172: Your answer isn’t correct. You’re way off base.
2005		L. Theroux Call of the Weird (2006) 214: This whole idea of it being a cult is so off-base.

2. (US black) adulterous, extra-marital.

1942

D. Burley N.Y. Amsterdam Star-News 15 Aug. 14: Few items have proved as juicy as this classic of off-base playing in dicty circles.

insane, crazy, confused, muddled, mistaken, behaving wildly.

1882		G.W. Peck Peck’s Sunshine 42: The Boston lady held up her hands in holy horror, and was going to explain to the speaker how she was off her base.
1885		Illus. Police News 10 Oct. 3/4: ‘This is a fish story,’ she replied, with natural indignation. ‘The fellow who wrote it is way off his base’.
1895		E. Townsend Chimmie Fadden Explains 10: Dat’s de way wid women; if you try t’ find out what dey do or don’t do tings for, you’re worse off your base dan before.
1905		G.W. Peck Peck’s Bad Boy Abroad 35: It wouldn’t be strange, after all he has gone through [...] if he was a little off his base.
1910		E. Rosen In the Foreign Legion 75: ‘I’m a bit off my base. I very often am, you know’.
1911		‘Sing Sing No. 57,700’ My View on Books in N.Y. Times Mag. 21 May 7/4: She gets off her base about the main squeeze [...] She croaks to save him at the finish.
1920		S. Lewis Main Street (1921) 298: You’re way off your base when you say I only like one kind of house!
1927		V. Samuels ‘Baseball Sl.’ in AS II:5 256: The expressions in general use, ‘to be off one’s base,’ ‘to get one’s innings,’ ‘to get on to a person’s curves,’ derive from baseball.

see under third adj.