knucklehead vs pillock

knucklehead and pillock both are nouns.

Word	Noun	Adjective	Verb	Adverb
knucklehead	Yes	No	No	No
pillock	Yes	No	No	No

As nouns, pillock is a hypernym of knucklehead; that is, pillock 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
pillock: a person who is not very bright

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

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