1850, "frenzied passion," from Latin oestrus "frenzy, gadfly," from Greek oistros "gadfly, breeze, sting, mad impulse," perhaps from a PIE *eis, forming words denoting passion (cf. Avestan aešma- "anger," Lithuanian aistra "violent passion," Latin ira "anger"). First attested 1890 with specific meaning "rut in animals, heat." Earliest use (1690s) was for "a gadfly." Related: Estrous (1900).
The periodic state of sexual excitement in the female of most mammals, excluding humans, that immediately precedes ovulation and during which the female is most receptive to mating; heat.
A regularly recurring period in female mammals other than humans during which the animal is sexually receptive. Estrus occurs around the time of ovulation. Also called heat
