phenytoin vs hydantoin

phenytoin and hydantoin both are nouns.

Word	Noun	Adjective	Verb	Adverb
phenytoin	Yes	No	No	No
hydantoin	Yes	No	No	No

As nouns, hydantoin is a hypernym of phenytoin; that is, hydantoin is a word with a broader meaning than phenytoin:

phenytoin: an anticonvulsant drug (trade name Dilantin) used to treat epilepsy and that is not a sedative
hydantoin: any of a group of anticonvulsant drugs used in treating epilepsy

phenytoin (noun)	hydantoin (noun)
an anticonvulsant drug (trade name Dilantin) used to treat epilepsy and that is not a sedative	any of a group of anticonvulsant drugs used in treating epilepsy