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.

Retain one's composure and poise, as in Billy keeps his cool, no matter what the situation. This slangy usage dates from the mid-1900s, as do the antonyms blow one's cool and lose one's cool, as in Try not to blow your cool in front of the team, or Dad lost his cool when he saw Jim playing with matches. Also see keep cool.