'unornamented' originates from English, composed of the prefix 'un-' (a native Old English/Old Germanic element meaning 'not') plus the noun 'ornament' (ultimately from Latin 'ornamentum'), with the adjectival suffix '-ed'.

'ornament' came into English via Old French 'ornement' from Latin 'ornamentum' (from the verb 'ornare' meaning 'to adorn'); 'ornament' then formed adjectives like 'ornamented', and the negative prefix 'un-' was added to produce 'unornamented'.

Initially the root 'ornare' and related words referred to 'equipping' or 'adorn(ing)'; over time the combined form 'unornamented' came to mean 'not decorated' or 'plain' in modern English.