early 15c., relapsen, "renounce" (a vice, etc.), a sense now obsolete; 1560s as "fall into a former (bad) state or practice," from Latin relapsus, past participle of relabi "slip back, slide back, sink back," from re- "back" (see re-) + labi "to slip" (see lapse (n.)). Related: Relapsed; relapsing.
mid-15c., "a falling back into error or wrongdoing, moral backsliding," from relapse (v.) or else from Medieval Latin relapsus. In medicine, "a falling back into a disease or symptom during or after convalescence," from 1580s.
updated on June 22, 2021