Green’s Dictionary of Slang

1. (orig. US Und.) to calm (someone) down; often as imper. cool out!; also to pacify another; thus cooling-out adj.

1912		Ade Knocking the Neighbors 118: His Seconds would cool him out and rub him with Witch Hazel.
1940		D. Maurer Big Con 48: Louis has already solicitously begun the ‘cooling out’ process.
1953		A.J. Liebling Honest Rainmaker (1991) 123: Dynamite was irascible, and we thought it best to let him cool out.
1967		L. Bruce Essential Lenny Bruce 32: How’m I just gonna cool this guy out?
1976		Jenkins & Shrake Limo 233: I tried to cool her out. Like give her the water pipe to get straight, but she starts cryin’, man.
1981		W.D. Myers Hoops 66: ‘Hey man, cool out,’ she said. ‘I didn’t mean nothing’.
1985		O. Hawkins Chili 70: I took a deep breath [...] to cool myself out.
1994		M. Montague Dread Culture 92: Wah yuh doin man? [...] We inna nuff trouble widout tek on more. Cool out, man.
2000		Guardian Rev. 21 Apr. 9: Sprague, who had a bad trip [...] had to be cooled out with a handful of valium.
2012		W. Keyser ‘Carny Lingo’ in http://goodmagic.com 🌐 Cool Out — Convincing a mark that he has not been taken.

2. (W.I.) to take a rest from work by lying in the shade of a tree.

1979

E. Lovelace Dragon Can’t Dance (1998) 66: I just cooling out. You want a cigarette?

3. to relax.

1950		E. Hemingway letter 9 July in Baker Sel. Letters (1981) 701: I shouldn’t start fixing the stories until I cool out.
1966		H.S. Thompson letter 20 July in Proud Highway (1997) 578: I needed about a week of total degeneration to cool out the system.
1978		R. De Christoforo Grease 89: Sandy was cooled out.
1982		Eble Campus Sl. Fall 1: cool out – to have a quiet evening.

4. (US Und.) of a confidence man, to avoid the victim from whom the money has been extracted.

1965

J. Thompson Texas by the Tail (1994) 122: This cooling out on a chump, of course, is routine in any hustle.

5. to make manageable.

1963		J. Cohen Essential Lenny Bruce 285: We must have some laws to restrict the behavior – to cool the people out.
1977		M. Herr Dispatches 5: One 4th Division Lurp [...] took his pills by the handful [...] they cooled things out just right for him.