serpent vs diapsid reptile

serpent and diapsid reptile both are nouns.

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

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

serpent: limbless scaly elongate reptile; some are venomous
diapsid reptile: reptile having a pair of openings in the skull behind each eye

Other hypernyms of serpent include diapsid.

serpent (noun)	diapsid reptile (noun)
limbless scaly elongate reptile; some are venomous	reptile having a pair of openings in the skull behind each eye
an obsolete bass cornet; resembles a snake
a firework that moves in serpentine manner when ignited