'nonforfeitability' is a Modern English formation composed of the prefix 'non-' (from Latin 'non', meaning 'not'), the root 'forfeit' (from Old French 'forfet/forfait', referring to a penalty or an act of losing rights), and the noun-forming suffix '-ability' (from Old French/Latin 'abilitas', meaning 'capacity or tendency').

'forfeit' entered English via Old French during the Middle English period as 'forfet/forfait'; later, English productivity added the prefix 'non-' and the suffix '-ability' to create abstract nouns such as 'nonforfeitability' in Modern English.

Originally the components expressed 'not' + 'penalty/forfeiture' + 'capacity'; over time the compound has taken the specific meaning 'the state or quality of not being liable to forfeiture.'