What is synonym of probity?

honesty, moral rectitude, etc come close. probity carries the connotation of being the positive attribute or being observably morally and legally correct and fair in every particular of every transaction. Because it carries so much implied meaning, the best use of the Word probity is somewhat confined. Your choice of a synonym depends on what you're describing and what connotations you want to drag in. You might want anything from forthright to transparent, or prim, or even prig if you don't admire someone who took it too far and made the virtue into a vice.