'unpleasantness' originates from the word 'unpleasant', which is derived from the prefix 'un-' meaning 'not' and 'pleasant' from Old French 'plaisant', meaning 'pleasing'.

'unpleasant' changed from the Old French word 'plaisant' and eventually became the modern English word 'unpleasant'.

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