're-registrant' originates from the prefix 're-' meaning 'again' and the word 'registrant' from Latin 'registrare', meaning 'to record'.

'registrare' transformed into the French word 'registrer', and eventually became the modern English word 'register', with 're-' added to indicate repetition.

Initially, it meant 'to record again', but over time it evolved into its current meaning of 'a person who registers again'.