'unsplittability' originates from Modern English formation, specifically from the adjective 'unsplittable' plus the nominalizing suffix '-ity', where 'un-' meant 'not', 'split' meant 'to divide or cleave', '-able' meant 'capable of', and '-ity' meant 'state or condition'.

'unsplittability' changed from the adjective 'unsplittable', which itself was formed from the verb 'split' (Middle English 'spleten/splittan') and the negative prefix 'un-'; 'split' goes back to Germanic roots and developed into modern English 'split', from which the adjective and then the noun were derived.

Initially, the root 'split' meant 'to divide or cleave', and over time the derived formation 'unsplittability' came to mean the specific condition or quality of 'not being able to be split'.