oestrogen [E20th] Oestrogen (spelt estrogen in American English) is a hormone which gets its name, coined in 1927 by the pharmaceutical company that patented it, from oestrus (estrus), the period a female animal is ready to mate, combined with the suffix -(o)gen ‘producing’. Oestrus itself goes back via Latin to Greek oistros ‘gadfly, sting’, hence ‘frenzy, mad impulse’.