* It's a combination of "knuckle" and "head." This suggests it's a descriptive term, likely referring to someone who is either:
* Clumsy or foolish: The image of a person bumping their head with their knuckles evokes a sense of clumsiness and lack of coordination.
* Stubborn or dense: The term could also suggest a hardness of the head, similar to how we might refer to someone with a "thick skull" or a "hard head."
* Earliest known use: The earliest recorded use of "knucklehead" dates back to the late 19th century, appearing in American slang.
* Similar words: The word "knucklehead" is closely related to similar terms like "blockhead," "bonehead," and "dullard," all of which imply a lack of intelligence or common sense.
While the precise origin isn't definitively documented, its construction and early usage suggest it arose from the common imagery of clumsiness and foolishness associated with bumping one's head.