To cool down is to become less hot, or less angry. Let the engine cool down, cool down after a run, wait for him to cool down.
In sport it names the gentle exercise done at the end of a session, which has a purpose of its own. The angry sense works the same way, since both are a slow return to normal.
1phrasecool downTo become less hot — or less angry.
“Give him an hour to cool down before you raise it again.”
cool down is a phrase.
Practised in Phrasal Verbs