At any time; at an unspecified time in the past, present, or future; an archaic or dialectal word for 'whenever'.
From 'any' (Old English 'ænig') + 'when' (Old English 'hwonne,' meaning at what time); a formation parallel to 'anywhere' and 'anyhow'.
Most English speakers have abandoned 'anywhen' in favor of 'whenever' or 'at any time,' but Scottish and Northern English dialects kept it alive, showing how older words survive in regional speech.
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