Someone considered stupid or foolish; also, the tiny round head of a pin.
From 'pin' + 'head,' literally the top of a pin. Used figuratively since the 1600s to mean someone small-minded or of little intelligence, comparing their intellect to the tiny pinhead.
Pinhead is a perfect example of how we create insults through size metaphors—small-headed means small-brained means stupid. This happens constantly: airhead, blockhead, bonehead, fathead. We equate brain size with intelligence without realizing it.
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