dunderhead vs dullard

dunderhead and dullard both are nouns.

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

As nouns, dullard is a hypernym of dunderhead; that is, dullard 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
dullard: a person who is not very bright

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

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