Backslide

To draw back or apostatize in matters of religion (Acts 21:21; 2 Thess 2:3; 1 Tim 4:1). This may be either partial (Prov 14:14) or complete (Heb 6:4–6; Heb 10:38, Heb 10:39). The apostasy may be both doctrinal and moral.

From Easton’s Bible Dictionary (1897), by Matthew George Easton.