Many, many years ago, one of my teachers delighted in calling his less intellectually gifted pupils “chuckleheaded idiots”. A nicely rhythmic expression, in real life it would have been likely to get him a punch on the nose. We slaves to mortarboarded masters didn’t have that option.
English speakers have been able to call a stupid or foolish person a chucklehead at least since the early eighteenth century. For most of its life it was a local or dialect word, albeit widely distributed, not used by serious English writers unless they wanted to evoke the earthy language of a son of toil. Americans were more egalitarian:
There wasn’t a human being in this town but knew that that boy was a perfect chucklehead; perfect dummy; just a stupid ass, as you may say. Everybody knew it, and everybody said it. Well, if that very boy isn’t the first lawyer in the State of Missouri to-day, I’m a Democrat!
Life On The Mississippi, by Mark Twain, 1883.
It used to be assumed that the chuckle part represented the sunny attitudes of a person so dim-witted that he was unable to appreciate the horrors of everyday life and so lived happily within the narrow confines of his own mind. The first edition of the Oxford English Dictionary thought so but the experts now disagree.
They say it’s from chuck in the sense of a chock, which is really no more than a different spelling of the same word. Like chock, it could mean a lump of wood, but it could also be a piece of cheese or home-made cake or anything else small enough to hold in the hand. You might call it a chunk, which is another modification of the same word. We’re familiar with the chuck of a drill, a shaped chunk of metal, but might not make the connection with chuck steak, which is etymologically a lump of meat. So chucklehead is a relative of bonehead, knucklehead, blockhead and other insulting assertions that the head of the addressee is solid right through.
Might the experts who equated chuckleheadedness with laughter have been thinking of the origin of chuckle? That, too, comes from chuck, plus the -le ending that marks a repeated action. This chuck is a different word, however, probably imitating the sound of a contented chicken (it’s in origin the same word as cluck). The theory that chucklehead came from chuckle might have implied the person so described was a birdbrain. But it isn’t so.