1640s (as a past participle adjective, 1570s), from Late Latin deterioratus, past participle of deteriorare "get worse, make worse," from Latin deterior "worse, lower, inferior, meaner," contrastive of *deter "bad, lower," from PIE *de-tero-, from demonstrative stem *de- (see de). Originally transitive in English; intransitive sense is from 1758. Related: Deteriorated; deteriorating.