BACKSLIDE

[verb] [I] [past:] backslid - to go back to doing something bad when you have been doing something good, esp. to stop working hard or to fail to do something that you had agreed to doWe were making good progress on this project for a while, but now things have begun to backslide and we're behind schedule.I've been trying to lose weight by going on a diet, but I've been backsliding a bit recently.The government seems to be backsliding over/on/from (= failing to keep) its promise not to raise taxes.