Also ˈestrum (ˈɛstrəm
2. the period of this when the female will accept mating with the male, characterized by changes in the sex organs
Webster’s New World College Dictionary, Fourth Edition, compiled by the
editors of Webster’s New World Dictionaries. Copyright © 2010 by Houghton
Mifflin Harcourt. Published by Houghton Mifflin Harcourt. All rights reserved.
Word origin of 'estrus'ModL < L oestrus, gadfly, horsefly, frenzy < Gr oistros, gadfly, sting, frenzy < IE base *eis-, to move violently > ON eisa, to rush on, L ira, ire, Lith aistra, violent passion