Green’s Dictionary of Slang

1. psychoanalysis or psychology.

1921		T. Thursday ‘Hail the Professor’ in Top-Notch 1 Sept. 🌐 He is working on his new theory of psycho—er—and stuff like that.
1921		R. Macaulay Dangerous Ages 102: ‘Psycho-analysis, I mean.’ ‘Oh, psycho [...] Not that insomnia is always a case for psycho, you know.’ [OED].
1960		Times 25 June 12/3: The mind was so important in this work [i.e. radionics] that it excluded all physical considerations. They were coming down solidly on the psycho side, but not the psychic side.

2. a psychopath.

1946		Mezzrow & Wolfe Really the Blues 180: I first began switching to the psycho kick when I landed a job at the Woodmansten Inn.
1951		E. Hemingway letter 5 Mar. in Baker Sel. Letters (1981) 721: He has the psycho’s urge to kill himself.
1965		L. Bruce How to Talk Dirty 47: Drugs users are sick, emotionally immature, degenerates, psychos, unstable.
1978		R. Caron Go-Boy! 254: The two cons who dealt themselves in were considered [...] psychos, unstable personalities who would kill in the blink of an eye.
1987		Ice-T ‘Hit the Deck’ 🎵 Evil cuts the records like a psycho with a switchblade.
1993		I. Welsh Trainspotting 80: One fat cunt ay the group of psychos goes up tae this other group ay guys [...] n sticks the heid oan one ay them.
2004		K. Bruen ‘Fade To . . . Brooklyn’ in Brooklyn Noir 310: A quiet psycho is a fearsome animal.
2007		L. Redhead Cherry Pie [ebook] I wasn’t the one who had behaved like a complete psycho.
2010		(con. 1973) C. Stella Johnny Porno 127: Got smart and listened for a change [...] Not that it makes him any less of a psycho.
2010		L. Redhead Thrill City [ebook] The car could be that psycho coming back.
2012		(con. 1980s) I. Welsh Skagboys 42: He likes me; all psychos seem tae.
2015		S. King Finders Keepers (2016) 102: I’m sorry as hell. At least they caught the psycho before he could do any more damage.
2020		S.A. Crosby Blacktop Wasteland 230: A movie-loving hillbilly psycho.

3. an insane, strange or eccentric person.

1947		(con. 1944) J.H. Burns Gallery (1948) 4: He’d thought for a long time anyhow that he was going to crack, and trenchfoot was a more honorable way of doing it than becoming a psycho.
1959		C. MacInnes Absolute Beginners 11: The Wiz has for all oldies just the same kind of hatred psychos have for Jews or foreigners or coloureds.
1966		T. Keyes All Night Stand 76: We only had an eccentric landlord and not a houseful of psychos.
1978		R. Price Ladies’ Man (1985) 240: I don’t want to deal with no psychos tonight.
1989		T. Blacker Fixx 305: Psychos, junkies, banged-up teenies.
1990		S. Morgan Homeboy 67: Their failure to apprehend real criminals like the psycho who murdered Gloria Monday.
1999		Indep. on Sun. 27 June 9: Is Dame Joan Collins a secret psycho?
2001		Guardian 12 Mar. 5: Only one third thought it was unacceptable to call people ‘schizo’ or ‘psycho’.
2012		IOL Cape Western News (SA) 14 Feb. 🌐 He is a psycho. He needs to go back to school, perhaps he will grow and become a good citizen.
2018		G. Disher Kill Shot [ebook] Kramer was already reaching out to some of the psychos in the joint.
2019		N. Walker Cherry 219: She was [...] yelling like the world’s most beautiful psycho.

4. a psychiatrist, psychologist, psychoanalyst.

1949		N. Algren Man with the Golden Arm 204: Look out for the major. He’s a psycho.
1956		‘Raymond Thorp’ Viper 72: I went to see the psycho, a nice little cat who gave me squares to fit into holes.
1962		P. Crump Burn, Killer, Burn! 337: You sound frustrated [...] a candidate for a psycho’s couch.
1974		H. Levin Bandiet 75: We would be interviewed by the psychos.
1982		G. Newbold Big Huey 165: He asked the Justice psychologist to do a report [...] The psycho interviewed me [...].
1996		J. Cameron It Was An Accident 170: All the stuff I got off the psychos back when I was a young offender.

5. a psychiatric ward.

1978		H. Selby Jr Requiem for a Dream (1987) 223: Dr Reynolds diagnosed her as a paranoid shizophrenic and sent her to psycho.
1992		S.L. Hills Tragic Magic 96: I was in D-2 psycho, which is a lock-in.

6. (N.Z. prison) a firearm.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 148/1: psycho n. a firearm.