hammerhead vs pudding head

hammerhead and pudding head both are nouns.

Word	Noun	Adjective	Verb	Adverb
hammerhead	Yes	No	No	No
pudding head	Yes	No	No	No

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

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

hammerhead (noun)	pudding head (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