sea hare vs gastropod

sea hare and gastropod both are nouns.

Word	Noun	Adjective	Verb	Adverb
sea hare	Yes	No	No	No
gastropod	Yes	No	No	No

As nouns, gastropod is a hypernym of sea hare; that is, gastropod is a word with a broader meaning than sea hare:

sea hare: naked marine gastropod having a soft body with reduced internal shell and two pairs of ear-like tentacles
gastropod: a class of mollusks typically having a one-piece coiled shell and flattened muscular foot with a head bearing stalked eyes

Other hypernyms of sea hare include univalve.

sea hare (noun)	gastropod (noun)
naked marine gastropod having a soft body with reduced internal shell and two pairs of ear-like tentacles	a class of mollusks typically having a one-piece coiled shell and flattened muscular foot with a head bearing stalked eyes