estrous (ˈestrous) or estrual (ˈɛstruːəl, ˈiːstruːəl)
adjective
estrus in American English
(ˈɛstrəs; British; usually ˈistrəs)
noun
1.
the periodic sexual excitement of most female placental mammals, corresponding to rut in males; heat
2.
the period of this when the female will accept mating with the male, characterized by changes in the sex organs
Also ˈestrum (ˈɛstrəm)
Word origin
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