- estrus
- 1850, from L. oestrus "frenzy, gadfly," from Gk. oistros "gadfly, breeze, sting, mad impulse" (probably cognate with Lith. aistra "violent passion," L. ira "anger"). Earliest English sense is of "frenzied passion;" first attested 1890 with meaning "rut in animals, heat." Related: Estrous.