'inassignability' originates from English, formed by the negative prefix 'in-' + 'assignability'. 'assign' ultimately comes from Latin 'assignare', where 'ad-' (later assimilated to 'as-') meant 'to, toward' and 'signare' meant 'to mark' or 'to sign'; the suffixes '-able' and '-ity' form a noun meaning 'the quality of being able to be assigned'.

'assign' entered English via Old French 'assigner' from Late Latin 'assignare'. From 'assign' the adjective 'assignable' and the noun 'assignability' developed in Modern English; 'inassignability' is a later formation by prefixing 'in-' to negate 'assignability'.

Originally, roots related to 'assign' meant 'to mark out, allot, or give.' Over time 'assignability' came to mean 'able to be assigned or transferred,' and 'inassignability' accordingly denotes 'not able to be assigned or transferred.'