'unforeseeably' originates from English, specifically from the word 'unforeseeable' with the adverbial suffix '-ly', where 'un-' means 'not', 'foresee' means 'to see beforehand', and '-able' means 'capable of'.

'unforeseeable' was formed in English by combining 'un-' + 'foresee' + '-able', and 'unforeseeably' was later formed by adding '-ly' to create the adverb. It eventually became the modern English word 'unforeseeably'.

Initially, it meant 'in a manner that cannot be foreseen', and this meaning has remained consistent in modern usage.