Antonyms for Heat (opposite meaning)
WordNet sense 1 (applies to nonhuman mammals: a state or interval of sexual inactivity between two periods of estrus):
anestrusWordNet sense 2 (the absence of heat):
cold, coldness, frigidity, frigidness, low temperatureWordNet sense 3 (loose heat):
coolFrom the ODE community, based on WordNetadd/edit