Dictionary:

estrous

  (ĕs'trəs)

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Of, relating to, or being in estrus.

Relating to or being in estrus.

Pertaining to or emanating from estrus.

• e. cycle — one of the two types of reproductive cycles, the other is the menstrual cycle of humans and primates. Regularly occurring periods during which the female is sexually active and receptive, estrus, separated by periods in which there is no sexual receptivity. This period is divided, on the basis of ovarian activity into metestrus (early corpus luteum development), diestrus (mature corpus luteum) and pro-estrus (period of follicle development). The details of estral activity are summarized in Table 17.

The adjective has one meaning:

Meaning #1: (of lower mammals) showing or in a state of estrus; in heat
  Antonym: anestrous (meaning #2)