'unpleasant' originates from Middle English, specifically the word 'plesaunt,' where 'un-' meant 'not' and 'plesaunt' meant 'pleasing.'

'plesaunt' transformed into the modern English word 'pleasant,' and with the prefix 'un-' added, it became 'unpleasant.'

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