What is Cool down ?
Cool down is (verb) 1. to make something cool or to become cool Although it is very hot in the desert during the daytime, it always cools down in the evening. This coffee is too hot – I’m waiting for it to cool down a bit. 2. to calm someone, or to become calmer He was furious with his secretary, but after a while he cooled down. We tried to cool him down but it just made him more angry.
source: Easier English, Student Dictionary Upper Intermediate Level