'holier-than-thou' originates from the English phrase 'holier than thou,' where 'holier' meant 'more holy' and 'thou' was an archaic form of 'you.'

'holier than thou' was used in religious contexts to describe someone who believed themselves to be more pious than others, and eventually became the modern English phrase 'holier-than-thou.'

Initially, it meant 'more holy than you,' but over time it evolved into its current meaning of 'self-righteous or morally superior.'