When something retrogresses, it does not merely go back. It goes back to an earlier state that is worse — a sick person who was getting better and then slips; a country that had more open talk and then shuts it down; a skill that fades because you stopped using it. The word already judges the move: this is a fall, not a homecoming. Though actually, you will almost never hear it in ordinary conversation. People say get worse, go backwards, or regress. Retrogress is a formal, rather bookish verb. Even in careful writing, many people reach first for retrograde (a retrograde step). Use this one when you want the verb itself, and when you mean loss of ground, not simply return.

倒退