To talk excessively about something or to discuss at length; an archaic or dialectal word meaning to exhaust by talking.
From 'be-' (prefix intensifying the action) + 'talk.' The 'be-' prefix was productive in Old and Middle English for creating intensive or completive verbs, though most such formations have died out.
The 'be-' prefix is a time-traveling feature of English—words like 'bedazzle,' 'besmirch,' and 'befriend' show it's still alive, but 'betalk' reminds us that medieval speakers could add 'be-' to almost any verb to mean 'do it thoroughly' or 'do it too much.'
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