An archaic or dramatic command to go away or leave; 'be gone' (begone as one word).
From Old English 'be' (be) + 'gān' (go). It's literally a command form: 'Be gone' = 'have yourself departed.' Archaic and poetic today.
This word survives mainly in Shakespeare and fantasy books now, but it shows how English used to use 'be' as an imperative verb. You'll never hear someone actually say 'begone!' in real life—it's purely theatrical.
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