'unheroism' originates from English, specifically formed from the prefix 'un-' (Old English 'un-') meaning 'not' and the noun 'heroism' (from 'hero' + the suffix '-ism'), where 'hero' ultimately comes from Greek 'hērōs' meaning 'demigod' or 'hero'.

'hero' was borrowed from Greek 'hērōs' into Latin as 'heros' and passed into Middle English as 'hero'; the abstract noun 'heroism' was formed in English with the suffix '-ism', and the negative prefix 'un-' was later attached to create 'unheroism'.

Initially, the construction simply signified 'not heroism' as a literal negation; over time it has also come to be used to describe 'cowardice' or specific failures to act heroically in context.