'unchallengeable' originates from the prefix 'un-' (Old English 'un-') combined with 'challengeable', which derives from 'challenge' from Old French 'chalonge' where 'chalonge' came ultimately from Latin 'calumnia' meaning 'false accusation'.

'unchallengeable' formed in modern English by adding the adjectival suffix '-able' to 'challenge' (from Old French 'chalonge'), producing 'challengeable' in later Middle English, and then prefixing with Old English 'un-' to create 'unchallengeable'.

Initially related to the notion of 'accusation' or 'challenge' (from Latin 'calumnia' meaning 'false accusation'), the element developed into the sense of 'to dispute or contest', and over time 'unchallengeable' came to mean 'not able to be disputed' in modern usage.