es·tri·ol noun alsooes·tri·ol\ˈeˌstrīˌȯl, eˈs-, -īˌōl\ (-s) Etymology: blend of estrin, oestrin and -triol : a white crystalline estrogenic hormone that is a phenolic steroid glycol C18H24O3 and is usually obtained from the urine of pregnant women — called also theelol