to become less hot, or to make someone or something become less hot

She waited until her coffee had cooled down before taking a sip. 她一直等到咖啡凉下来才抿了一小口。

We went for a swim to cool off. 我们去游泳好凉快一下。

to stop feeling angry or to stop someone else feeling angry after an argument

Leave her to cool off and then talk to her. 让她一个人冷静冷静，然后再跟她谈。