A rounded or lump-shaped head; also a derogatory term for a stupid or thick-headed person.
Compound of 'cob' (a rounded lump) and 'head.' The derogatory meaning evolved as other round-shaped insults did, following a pattern of linking physical shape to perceived intelligence.
Medieval insults were oddly creative—'cobhead' was just one of dozens of shape-based insults (blockhead, meathead, birdbrain), showing how people have always used physical metaphors to mock others!
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