oestrus

‖n. [ L., a gadfly; also, frenzy, fr. Gr. &unr_; gadfly; hence, sting, fury, insane desire, frenzy. ] 1. (Zool.) A genus of gadflies. The species which deposits its larvae in the nasal cavities of sheep is oestrus ovis. [ 1913 Webster ]

2. A vehement desire. [ 1913 Webster ]

3. Specifically: (Physiol.) The periodical sexual impulse of animals; the period during which female animals are most receptive to males; heat; rut. [ 1913 Webster +PJC ]