cool

Concise Oxford English Dictionary © 2008 Oxford University Press:
cool/kuːl/

▶adjective

• 1 of or at a fairly low temperature.

  ■ (especially of clothing) keeping one from becoming too hot.

• 2 not excited, anxious, or emotional.

  ■ unfriendly or unenthusiastic.

  ■ (of jazz) restrained and relaxed.

• 3 informal fashionably attractive or impressive.

  ■ excellent.

  ■ used to express acceptance or agreement.

• 4 (a cool ——) informal used to emphasize the size of a sum of money: they pocketed a cool $1 million each.

▶noun (the cool) a cool temperature, place, or time. ▶verb

• 1 become or make less hot.

• 2 become less emotional or enthusiastic.

• 3 (cool out) informal relax: a dreamy spot where you could cool out and detox.

– phrases
keep (or lose) one's cool informal maintain (or fail to maintain) a calm and controlled attitude.

– derivatives
coolish adjective,
coolly adverb,
coolness noun.

– origin OE cōl (n.), cōlian (v.), of Gmc origin; rel. to cold.