'unusual' originates from the Latin word 'usualis', where 'un-' meant 'not' and 'usualis' meant 'customary'.

'usualis' transformed into the Old French word 'usuel', and eventually became the modern English word 'usual', with 'un-' added to form 'unusual'.

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