1
general::
Phrase(s): keep one’s cool
Inf. to remain calm and in control. • Relax, man! Just keep your cool. • It’s hard to keep your cool when you’ve been cheated., Phrase(s): keep cool
Inf. to stay calm and undisturbed. • Relax, man, keep cool! • If Sally could just keep cool before a race, she could probably win.
McGrawhill's American Idioms And Phrasal Verbs
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general::
Also, keep a cool head;stay cool;be cool;take it cool. Remain calm and under control, as in Keep cool, they'll soon show up, or Be cool, the surprise is not spoiled, or You have to keep a cool head in these volatile situations, or Sit tight, take it cool, they won't bother you again. All these terms employ cool in the sense of "not heated by strong emotion," a usage dating from the late 1300s or even earlier. The first three expressions are colloquial and date from the second half of the 1800s; both of the last two are slang, and the very last (take it cool) is the oldest, first recorded in 1841. Also see KEEP ONE'S COOL; PLAY IT COOL.
American Heritage Idioms