'nonappealability' originates from Modern English, specifically formed from the prefix 'non-' (from Latin 'non' meaning 'not'), the verb 'appeal' (ultimately from Latin 'appellare' via Old French 'apeler' meaning 'to call or address'), and the nominalizing suffix '-ability' (from Latin '-abilitas' meaning 'capacity, ability').

'nonappealability' was formed in Modern English by attaching the prefix 'non-' and the suffix '-ability' to the verb 'appeal'; 'appeal' changed from Old French 'apeler' (from Latin 'appellare') into Middle English forms and eventually into the modern English 'appeal', while '-ability' derives from Latin '-abilitas' passed through Old French/Anglo-Norman.

Initially 'appeal' meant 'to call' (and '-ability' meant 'capacity'); combined as 'appealability' this indicated the capacity to be appealed, and with the prefix 'non-' the compound evolved into the specialized legal meaning 'not subject to appeal' (i.e., incapable of being appealed).