'unassignability' originates from English, formed by adding the prefix 'un-' (meaning 'not') to 'assignability' (the quality of being assignable), where 'assign' comes from Latin 'assignare' meaning 'to mark out' or 'to allocate'.

'assignare' transformed into the Old French word 'assigner', which entered Middle English as 'assign', and later formed 'assignability'. The prefix 'un-' was added to create 'unassignability'.

Initially, 'assign' meant 'to allocate or designate', and 'assignability' meant 'the ability to be assigned'. Adding 'un-' changed the meaning to 'the inability to be assigned', which is the current meaning.