1
general::
Phrase(s): Cool it!
Inf. Calm down!; Take it easy! • Don’t get mad, Bob. Cool it! • Cool it, you guys! No fighting around here.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
1. Calm down, relax, as in John was beginning to seethe, but I told him to cool it. [Slang; c. 1950] 2. Stop what one is doing, especially stop talking or behaving conspicuously, as in We'd be wise to cool it until the scandal blows over. It is Also used as an imperative, as in Cool it! We'll be in trouble if anyone hears you. [Slang; c. 1950]
American Heritage Idioms