hammerhead vs dullard

hammerhead and dullard both are nouns.

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

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

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

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