diapsid reptile vs reptile

diapsid reptile and reptile both are nouns.

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

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

diapsid reptile: reptile having a pair of openings in the skull behind each eye
reptile: any cold-blooded vertebrate of the class Reptilia including tortoises, turtles, snakes, lizards, alligators, crocodiles, and extinct forms

Other hypernyms of diapsid reptile include reptilian.

diapsid reptile (noun)	reptile (noun)
reptile having a pair of openings in the skull behind each eye	any cold-blooded vertebrate of the class Reptilia including tortoises, turtles, snakes, lizards, alligators, crocodiles, and extinct forms