cayman vs crocodilian

cayman and crocodilian both are nouns.

Word	Noun	Adjective	Verb	Adverb
cayman	Yes	No	No	No
crocodilian	Yes	No	No	No

As nouns, crocodilian is a hypernym of cayman; that is, crocodilian is a word with a broader meaning than cayman:

cayman: a semiaquatic reptile of Central and South America that resembles an alligator but has a more heavily armored belly
crocodilian: extant archosaurian reptile

Other hypernyms of cayman include crocodilian reptile.

cayman (noun)	crocodilian (noun)
a semiaquatic reptile of Central and South America that resembles an alligator but has a more heavily armored belly	extant archosaurian reptile