'unhappy' originates from Old English, specifically the word 'unhæppi', where 'un-' meant 'not' and 'hæppi' meant 'fortunate or happy'.

'unhæppi' transformed into the Middle English word 'unhappi', and eventually became the modern English word 'unhappy'.

Initially, it meant 'not fortunate or lucky', but over time it evolved into its current meaning of 'not happy'.