knucklehead vs pudden-head

knucklehead and pudden-head both are nouns.

Word	Noun	Adjective	Verb	Adverb
knucklehead	Yes	No	No	No
pudden-head	Yes	No	No	No

As nouns, pudden-head is a hypernym of knucklehead; that is, pudden-head is a word with a broader meaning than knucklehead:

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

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

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