The Collaborative International Dictionary of English v.0.48:

Hydantoin \Hy*dan"to*in\, n. [Hydrogen + allantion.] (Chem.)
   A derivative of urea, C3H4N2O2, obtained from allantion, as
   a white, crystalline substance, with a sweetish taste; --
   called also glycolyl urea.
   [1913 Webster]