'resupply' is formed in English from the prefix 're-' (meaning 'again') + 'supply'. 'supply' originates from Latin 'supplēre', where 'sub/sup-' meant 'up to' or 'under' and 'plēre' meant 'to fill'.

'supplēre' in Latin became Old French (e.g. 'souppler'/'supplyer'), later entering Middle English as 'supplyen' and then modern English 'supply'. The verb 'resupply' was created by adding the productive prefix 're-' to 'supply' in later English.

Originally 'supply' carried the sense 'to fill (up)'. Over time it shifted toward the broader sense 'to provide what is needed', and 'resupply' specifically came to mean 'to provide again' or 'replenish'.