(of a nuclear reactor) that uses liquid sodium as a coolant

Calm and imperturbable, especially under pressure.

simple past tense and past participle of cool down

(intransitive) To become cooler, to be reduced in temperature. / (transitive) To cause the temperature of an item to decrease. / (intransitive) To become less agitated.

(idiomatic) to act cool

plural of cool kid

(idiomatic) calm and composed in a difficult situation.

(idiomatic) A calm, focused demeanor and mindset; a person having such characteristics.

(slang) Extremely cool.

(sociology) A tough, fearless, aloof attitude said to be adopted by black men as a coping mechanism to deal with racial oppression.