hammerhead vs stupid person

hammerhead and stupid person both are nouns.

Word	Noun	Adjective	Verb	Adverb
hammerhead	Yes	No	No	No
stupid person	Yes	No	No	No

As nouns, stupid person is a hypernym of hammerhead; that is, stupid person is a word with a broader meaning than hammerhead:

hammerhead: a stupid person; these words are used to express a low opinion of someone's intelligence
stupid person: a person who is not very bright

Other hypernyms of hammerhead include dolt, dullard, pillock, poor fish, pudden-head, pudding head, stupe, stupid.

hammerhead (noun)	stupid person (noun)
medium-sized live-bearing shark with eyes at either end of a flattened hammer-shaped head; worldwide in warm waters; can be dangerous	a person who is not very bright
the striking part of a hammer
a stupid person; these words are used to express a low opinion of someone's intelligence