1565-75; < Late Latindēteriōrātus made worse (past participle of dēteriōrāre), equivalent to Latindēterior worse (dē from + -ter- formative in adjectives of spatial orientation (cf. exterior, interior) + -ior comparative suffix) + -ātus-ate1
1570s, from L.L. deterioratus, pp. of deteriorare "get worse," from L. deterior "worse," contrastive of *deter "bad, lower," from PIE *de-tero-, from demonstrative stem *de- (see de). Originally transitive in English; intransitive sense is from 1758.