'oestrogen' originates from New Latin/Greek combining elements, specifically from Greek 'oistros' where 'oistros' meant 'gadfly, sexual frenzy' and the combining form '-gen' from Greek 'gennan' meant 'to produce'.

'oestrogen' was coined in the early 20th century as a scientific term (from 'oestrus' + '-gen' via New Latin/Modern scientific coinage) and entered English usage to name the hormones that induce oestrus; the spelling 'estrogen' is a later variant used especially in American English.

Initially it meant 'that which produces oestrus (sexual excitement)', but over time it evolved to mean the group of hormones that promote female characteristics and regulate reproduction.