A foolish or scatterbrained person; someone who is habitually confused or silly.
Compound of 'addle' (confused) + 'pate' (head/crown, from Latin 'patere'). It's a colorful variant on 'addlehead,' using 'pate' as an alternative word for head.
'Pate' is old-fashioned slang for head (think of a shiny pate), so 'addlepate' is like saying 'confused-head'—it's one of English's most creative ways of insulting someone's intelligence through their anatomy.
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