From Longman Dictionary of Contemporary Englishcool down phrasal verb1 to make something slightly colder, or to become slightly colder The air has cooled down a little now.cool somebody/something ↔ down A cold beer will cool you down.2 CALMto become calm after being angry After I cooled down I realized I had been wrong. → cool→ See Verb table
Examples from the Corpus
cool down• If the engine overheats, switch it off and do not start it again until it has cooled down.• It's been hot all summer, but it's finally starting to cool down a little. 