'unfavorable' originates from the prefix 'un-' meaning 'not' and the word 'favorable,' which comes from the Latin 'favorabilis,' meaning 'pleasing or agreeable.'

'favorabilis' transformed into the Old French word 'favorable,' and eventually became the modern English word 'favorable,' with 'un-' added to form 'unfavorable.'

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