'anywhen' originates from English, specifically a compound of the words 'any' + 'when', formed by combining 'any' (meaning 'one or some, no matter which') with 'when' (meaning 'at what time').

'any' comes from Old English 'ænig' and 'when' comes from Old English 'hwænne'; the compound 'anywhen' is a later English formation (recorded in Early Modern English and in dialectal/poetic uses) combining these elements.

Initially and historically it has been used to mean 'at any time'; this basic meaning has remained, though the form is now rare or archaic and more often replaced by phrases like 'at any time' or 'ever'.