dunderhead vs stupid

dunderhead and stupid both are nouns.

Word	Noun	Adjective	Verb	Adverb
dunderhead	Yes	No	No	No
stupid	Yes	Yes	No	No

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

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

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

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

dunderhead (adjective)	stupid (adjective)
	lacking or marked by lack of intellectual acuity
	lacking intelligence
	in a state of mental numbness especially as resulting from shock