'reassignable' originates from the Latin prefix 're-' (from Latin 're-' meaning 'again') combined with 'assignable', ultimately from Latin 'assignare', where 'ad-' meant 'to' and 'signare' meant 'to mark or sign'.

'assignare' in Latin passed into Old French as 'assigner' (or similar forms) and into Middle English as 'assignen'/'assign', and the modern English verb 'assign' took the prefix 're-' and the suffix '-able' to form 'reassignable'.

Initially related to 'assign' meaning 'to mark out or allocate', it evolved so that 'reassignable' now specifically means 'capable of being allocated or assigned again'.