Stilbestrol, or stilboestrol, also known as 4,4'-dihydroxystilbene or 4,4'-stilbenediol, is a stilbenoid nonsteroidal estrogen and the parent compound of a group of more potent nonsteroidal estrogen derivatives that includes, most notably, diethylstilbestrol (DES). The term "stilbestrol" is often used incorrectly to refer to DES, but they are not the same compound. Stilbestrol itself is an active estrogen but is less potent than DES and other derivatives.