Green’s Dictionary of Slang

1. sane.

1809		‘D. Knickerbocker’ Hist. N.Y. I viii: He would [...] say something about ‘deranging his ideas’; which made my wife believe sometimes that he was not altogether compos .
1859		C.J. Lever Davenport Dunn 48: [...] but ye see I wasn’t compos when I did it .
1897		Daily News 23 Feb. in Ware (1909) 39/1: It was stated that this was not the prisoner’s first appearance on a similar charge [i.e. of disturbing the peace], and a doctor had certified that he was not altogether compos.
1922		Joyce Ulysses 307: Compos your eye! says Alf, laughing. Do you know that he’s balmy?
1949		Wodehouse Mating Season 63: I wouldn’t say he was one of our great minds, but he’s perfectly compos.
1958		B. Hamilton Too Much of Water 158: Honestly, is he quite compos? [OED].
1966		J. Gielgud letter 6 Mar. in Mangan John Gielgud’s Letters (2004) 328: They are only half compos.
2004		N. ‘Razor’ Smith A Few Kind Words and a Loaded Gun 61: I was colder than a magistrate’s smile and completely compos.

2. sober.

1979

J. Morrow Confessions of Proinsias O’Toole 36: Punchy came in about tea-time while I was still reasonably compos.