're-equip' originates from Latin and Old French elements: the prefix 're-' comes from Latin 're-' meaning 'again', and 'equip' comes from Old French 'equiper' (earlier 'esquiper'), where 'equiper/esquiper' meant 'to fit out' or 'to prepare'.

'equip' developed from Old French 'esquiper'/'equiper' (used for fitting out ships and gear), passed into Middle/Modern French as 'équiper', and into English as 'equip'; the verb 're-equip' was formed by adding the Latin prefix 're-' to this verb to mean 'equip again'.

Initially the root 'equip' often had the narrower sense 'to fit out (a ship) or prepare for use'; over time it broadened to mean 'to supply with necessary equipment' in general, and 're-equip' came to mean 'to supply again' in the modern sense.