1550s, from French réjection (16c.) or directly from Latin reiectionem (nominative reiectio) "act of throwing back," noun of action from past participle stem of reicere (see reject). In 19c., it also could mean "excrement." Medical transplant sense is from 1954. In the psychological sense, relating to parenting, from 1931.[rejection etymology, rejection origin, 英语词源]