c.1200, "forgiveness or pardon (of sins)," from Old French remission "forgiveness (of sins), relief" (12c.), from Latin remissionem (nominative remissio) "relaxation, diminishing," lit. "a sending back, sending away," noun of action from past participle stem of remittere "slacken, let go, abate" (see remit). Used of diseases since early 15c.