'anoestrus' originates from New Latin, formed from the negative prefix 'an-' (from Greek 'an-') meaning 'not' and 'oestrus' (from Greek 'oistros') meaning 'gadfly' or 'sexual excitement'.

'anoestrus' was coined in scientific New Latin/Modern English by combining 'an-' + 'oestrus'; 'oestrus' entered English via New Latin from Greek 'oistros', and the combined form came into use in 19th-century veterinary and biological literature.

Initially it meant 'absence of oestrus or sexual excitement', and that core sense has remained essentially unchanged in modern usage.