'anoestrous' originates from New Latin, specifically from the elements 'an-' + 'oistros' (Greek), where 'an-' meant 'without' and 'oistros' meant 'gadfly; sexual frenzy'.

'anoestrous' developed from New Latin 'anoestrus' (formed from Greek elements) into scientific English usage; the element 'oistros' also appears in Latin/Neo-Latin forms such as 'oestrus/estrus', and the modern English adjective was adopted from these medical/veterinary terms.

Initially it meant 'without sexual frenzy' (literally lacking the 'oistros'), and over time it has remained specialized with the current meaning 'not in estrus; not in heat' in veterinary and biological contexts.