lunkhead vs stupid person

lunkhead and stupid person both are nouns.

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

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

lunkhead: 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 lunkhead include dolt, dullard, pillock, poor fish, pudden-head, pudding head, stupe, stupid.

lunkhead (noun)	stupid person (noun)
a stupid person; these words are used to express a low opinion of someone's intelligence	a person who is not very bright