'replenished' originates from Anglo-French, specifically the verb 'replenir,' where 're-' meant 'again' and 'plenir' meant 'to fill'; in English the past form was created by adding the suffix '-ed' to 'replenish,' ultimately from Latin 'plenus' meaning 'full'.

'replenir' (and Old French 'repleniss-') passed into Middle English as 'replenisshen'/'replenish' and eventually became the modern English 'replenish'; the form 'replenished' arose in English with the regular past suffix '-ed'.

Initially, it meant 'to make full again' and this sense has remained largely the same; as an adjective, 'replenished' came to mean 'having been refilled or restocked'.