A person who knows a lot about something or someone; an expert or knowledgeable observer.
From Scottish and Northern English dialect, from 'ken' (to know), which comes from Old English 'cennan' (to make known). It's much rarer in modern American English but remains used in British and Scottish contexts.
This word is basically dead in American English but alive and well in Scotland—it's a rare example of a genuine English word that didn't survive the Atlantic crossing and instead became locked into regional speech!
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