'unsweeten' originates from the prefix 'un-' meaning 'not' or 'reverse' and the word 'sweeten', which comes from Old English 'swēten', meaning 'to make sweet'.

'swēten' transformed into the Middle English word 'sweten', and eventually became the modern English word 'sweeten'. The prefix 'un-' was added to form 'unsweeten'.

Initially, 'sweeten' meant 'to make sweet', and 'unsweeten' evolved to mean 'to remove sweetness'.