'moralize' originates from Middle French, specifically the verb 'moraliser,' based on Late Latin 'morālis' (‘moral’) from Latin 'mōs, mōris' (‘custom, manner’) plus the verbal suffix '-ize.'

'moraliser' passed into Middle English as 'moralisen'/'moralize,' and eventually became the modern English word 'moralize.'

Initially, it meant ‘to explain allegorically or to apply a moral lesson,’ and later broadened to include ‘to preach about morals’ and ‘to try to improve conduct,’ as well as a modern pejorative sense of ‘to speak in a self-righteous way.’