The Collaborative International Dictionary of English v.0.48:
Relapse \Re*lapse"\ (r?-l?ps"), v. i. [imp. & p. p. Relapsed
(-l?pst"); p. pr. & vb. n. Relapsing.] [L. relapsus, p. p.
of relabi to slip back, to relapse; pref. re- re- + labi to
fall, slip, slide. See Lapse.]
1. To slip or slide back, in a literal sense; to turn back.
2. To slide or turn back into a former state or practice; to
fall back from some condition attained; -- generally in a
bad sense, as from a state of convalescence or amended
condition; as, to relapse into a stupor, into vice, or
into barbarism; -- sometimes in a good sense; as, to
relapse into slumber after being disturbed.
That task performed, [preachers] relapse into
3. (Theol.) To fall from Christian faith into paganism,
heresy, or unbelief; to backslide.
They enter into the justified state, and so continue
all along, unless they relapse. --Waterland.