estrous est·rous US/ˈɛstrʌs/ uncommon adjective 1. (of lower mammals) showing or in a state of estrus; in heat “the estrous state” “the estrous cycle” Antonymsanestrous Similarmonestrouspolyestrous WordNet 2.1 (Princeton University). CMU Pronouncing Dictionary. WordNet 2.1 Copyright Princeton University. All rights reserved.