Green’s Dictionary of Slang

cool v.2

1. [1900s; 1950s+] (orig. US) to calm down, to deal with a problem in a controlled manner, to resist confrontation.

2. [1950s+] to calm someone or some situation down.

3. [1950s+] to knock out.

4. [1960s] (US campus) to turn down a request for a date.

5. [1960s] (US Und.) of stolen goods, to remain hidden until police activity quietens.

6. [1960s] to render relaxed, happy.

7. [1960s+] (US) to postpone, to put off, to stop.

8. [1960s+] (US) of a criminal charge or disciplinary problem, to quash.

9. [1980s+] (US black/teen) to lounge around, to ‘hang out’.

10. [1980s+] to saunter.

11. see cool it v. (5)

In phrases

cool in (v.)

[1960s] (US teen) to inform.

cool it (v.)

see separate entry.

cool off

see separate entries.

cool out

see separate entries.

SE in slang uses

In phrases

cool-cock (v.) [var. on cold-cock v.]

[1930s–50s] (US) to knock unconscious.

cool-crack (v.) [var. on cold-cock v.]

[1940s] (US black) to knock unconscious.

cool one’s coppers (v.) [hot coppers n.]

1. [mid–late 19C] to take a drink to ease the parched throat caused by excessive drinking.

2. to stay in a place.

3. [1900s] (US) in fig use of sense 1, to calm down.

cool one’s jets (v.) (also calm one’s jets, cool one’s boots)

[1970s+] (orig. US) to calm down, to relax.

cool one’s role (v.)

[1960s] (US black/gang) to calm down.