'non-themed' originates from English, specifically the prefix 'non-' which derives from Latin 'non' where 'non' meant 'not', combined with 'theme' which derives from Greek 'thema' where 'thema' meant 'something laid down (a subject or proposition)'.

'non-' was used as a negative prefix in Latin ('non'); 'theme' entered English via Latin/Old French from Greek 'thema'; the compound 'non-themed' is a modern English formation created by combining the prefix 'non-' with the past-participle/adjectival form 'themed'.

Initially it simply meant 'not themed' (i.e., lacking a theme); over time this literal meaning has largely remained the same and is used to describe events, spaces, or items without an applied theme.