saurian vs diapsid

saurian and diapsid both are nouns.

Word	Noun	Adjective	Verb	Adverb
saurian	Yes	Yes	No	No
diapsid	Yes	No	No	No

As nouns, diapsid is a hypernym of saurian; that is, diapsid is a word with a broader meaning than saurian:

saurian: any of various reptiles of the suborder Sauria which includes lizards; in former classifications included also the crocodiles and dinosaurs
diapsid: reptile having a pair of openings in the skull behind each eye

Other hypernyms of saurian include diapsid reptile.

saurian (noun)	diapsid (noun)
any of various reptiles of the suborder Sauria which includes lizards; in former classifications included also the crocodiles and dinosaurs	reptile having a pair of openings in the skull behind each eye

saurian (adjective)	diapsid (adjective)
of or relating to lizards