to relapse into bad habits, sinful behavior, or undesirable activities.

an act or instance of backsliding

a backslide from his early training.

verb

apostatize , deviate , fall from grace , lapse , leave the straight and narrow , relapse , revert , sin , slip , regress , retrogress , break faith , degenerate , desert , deteriorate , ebb , fade , fail , fall , fall away , falter , fizzle , flag , flop , lessen , recidivate , renege , retrograde , return , sink , slump , wane , weaken , worsen

noun

backsliding , recidivation , recidivism , relapse