Meaning

noun applies to nonhuman mammals: a state or period of heightened sexual arousal and activity

noun type genus of the Oestridae: sheep botflies

originEtymology tree Proto-Indo-European *h₁eysh₂-der. Ancient Greek οἶστρος (oîstros)der. Latin oestrusbor. English oestrus Borrowed from Latin oestrus (“gadfly, sting, frenzy”), from Ancient Greek οἶστρος (oîstros), from Proto-Indo-European *h₁eys-, used to form words denoting passion; see also Latin īra (“anger”), Lithuanian aistra (“violent passion”), Avestan 𐬀𐬈𐬯𐬨𐬀 (aesma, “anger”).

Etymology from Wiktionary, CC BY-SA 3.0