'anestrus' originates from New Latin, specifically the prefix 'an-' meaning 'without' and 'estrus' meaning 'frenzy' or 'heat' (in the reproductive sense).

'anestrus' was formed in the late 19th century from the combination of 'an-' and 'estrus' in scientific Latin, and entered English medical terminology as 'anestrus'.

Initially, it meant 'absence of estrus', and this meaning has remained unchanged in modern usage, referring to the period of sexual inactivity.