backslide

To regress; to slip backwards or revert to a previous, worse state.

He felt better for a little while, before his condition started to backslide.

[…] Monna Brigida, who had backslided into false hair in Romola's absence, but now drew it off again and declared she would not mind being gray, if her dear child would stay with her.

To shirk responsibility; to renege on one's obligations or commitments.

Rich countries are backsliding on their commitment to agree to new WTO measures to help people in poor countries gain access to affordable medicines.

To revert back into a life of sin after being saved.

A backward regression; a reverting back to a worse state.

A dance move in which the feet are alternately slid back and the heels lifted, giving the illusion of walking forwards while actually moving backwards.