crocodile vs crocodilian

crocodile and crocodilian both are nouns.

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

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

crocodile: large voracious aquatic reptile having a long snout with massive jaws and sharp teeth and a body covered with bony plates; of sluggish tropical waters
crocodilian: extant archosaurian reptile

Other hypernyms of crocodile include crocodilian reptile.

crocodile (noun)	crocodilian (noun)
large voracious aquatic reptile having a long snout with massive jaws and sharp teeth and a body covered with bony plates; of sluggish tropical waters	extant archosaurian reptile