oestrus n applies to nonhuman mammals: a state or period of heightened sexual arousal and activity n type genus of the Oestridae: sheep botflies Usage(s) Anyway, she was in heat (oestrus for the technically minded) and thus had a male panda on either side in separate cages in the hope they might hit it off. Synonym(s) estrus heat rut Oestrus genus Oestrus Antonym(s) anestrus