'untidy' originates from Middle English, specifically the word 'untidi', where 'un-' meant 'not' and 'tidy' meant 'neat or orderly'.

'untidi' transformed into the modern English word 'untidy', and eventually became 'untidiest' as the superlative form.

Initially, it meant 'not neat or orderly', and this meaning has largely remained the same in modern usage.