estrus vs oestrus

estrus and oestrus both are nouns.

Word	Noun	Adjective	Verb	Adverb
estrus	Yes	No	No	No
oestrus	Yes	No	No	No

As nouns, estrus and oestrus are synonyms defined as:

estrus and oestrus: applies to nonhuman mammals: a state or period of heightened sexual arousal and activity

Other synonyms of estrus include heat, rut.

estrus (noun)	oestrus (noun)
applies to nonhuman mammals: a state or period of heightened sexual arousal and activity	applies to nonhuman mammals: a state or period of heightened sexual arousal and activity