're-enroll' originates from Latin and Old French elements: the prefix 're-' from Latin 're-' meaning 'again', and the verb 'enroll' from Old French 'enroller' (ultimately from Latin 'rotulus') where 'rotulus' meant 'roll' or 'list'.

'rotulus' changed into Old French forms such as 'rolle'/'rotle', then to Old French 'enroller' (to enter on a roll), then into Middle English as 'enrollen'/'enrolen' and eventually modern English 'enroll'. The modern compound 're-enroll' was formed by adding the Latin prefix 're-' ('again') to 'enroll'.

Initially it meant 'to enter a name on a roll or list'; over time 'enroll' came to mean 'to register', and with the prefix 're-' the compound came to mean 'to register again'.