'unforeseen-completion' originates from the combination of 'unforeseen' and 'completion'. 'Unforeseen' comes from Old English 'unforseon', where 'un-' meant 'not' and 'forseon' meant 'to see'. 'Completion' comes from Latin 'completio', where 'com-' meant 'together' and 'plere' meant 'to fill'.

'Unforeseen' changed from the Old English word 'unforseon' and 'completion' from the Latin word 'completio', eventually forming the modern English term 'unforeseen-completion'.

Initially, 'unforeseen' meant 'not seen or anticipated', and 'completion' meant 'the act of finishing'. Together, they evolved to mean 'an unexpected conclusion'.