'estrual' originates from Latin (via New Latin), specifically the word 'oestrus' (also seen as 'estrus'), where the Greek root 'oistros' meant 'gadfly' or 'frenzy'.

'estrual' changed from the Latin/New Latin term 'oestrus' (from Greek 'oistros') and entered English medical and biological usage as terms like 'estrus' and the adjective forms 'estrous' and 'estrual'.

Initially associated with the sense of frenzy or intense desire (from Greek 'oistros'), it evolved to the biological sense of the recurrent period of sexual receptivity in female mammals and thus the adjective meaning 'relating to estrus'.