'unacceptable' originates from the prefix 'un-' meaning 'not' and the word 'acceptable', which comes from Latin 'acceptabilis', meaning 'worthy of acceptance'.

'acceptable' changed from the Latin word 'acceptabilis' and eventually became the modern English word 'acceptable'.

Initially, it meant 'worthy of acceptance', but with the prefix 'un-', it evolved into its current meaning of 'not satisfactory or allowable'.