backslider

plural backsliders

1. A recidivist; one who backslides, especially in a religious sense; an apostate.

   She married him thinking to change his ways, and for a while he got religion, but he was ever a backslider; she soon began finding bottles stashed about the house.

   3 more examples

   At night the Red Elephant Tusk boomed and groaned among the hills, and the faithful waked and said: ‘The God of Things as They Are matures revenge against the backsliders.’

   1888, Rudyard Kipling, “The Judgement of Dungara”, in Black and White, volume 1, Folio Society, published 2004, page 382

   The choice of unilateralism by the US also exposed it to charges that it is a backslider on its WTO commitments.

   2009, Andrew F. Cooper, “Confronting Vulnerability through Resilient Diplomacy: Antigua and the WTO Internet Gambling Dispute with the United States”, in Andrew F. Cooper, Timothy M. Shaw, editors, The Diplomacies of Small States: Between Vulnerability and Resilience, Palgrave Macmillan, page 216

   You say that you “lapse into coupledom” on occasion. Do you get grief from fellow militant singles for being a backslider?

   2012 June 20, Brian Bethune, “Two against one: About coupledom and the stigma of being single”, in Maclean's

2. IrelandOne who will not do his work or shoulder his responsibilities.