Green’s Dictionary of Slang

1. (orig. US) an anarchic eccentric.

1977		Custom Car Nov. 43/2: To make sure I wouldn’t make too big a gonzo of myself [etc.].
1983		C. Heath A-Team 2 (1984) 75: Show this gonzo we mean business!
2000		Indep. Rev. 11 Feb. 14: A forthcoming biography of rock’s great gonzo chronicler Lester Bangs.

2. (Aus.) used as a nickname for one who has a notably large nose.

1995

P. Vautin Turn It Up! 136: I’ve got another mate, Gonzo. So called because he’s got a hooter so big you could hide buried treasure in it.

3. (N.Z. prison) a homosexual.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 80/1: gonzo n. a homosexual.