Is it ensure, insure, or assure?
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.
deteriorate de·te·ri·o·rate (dĭ-tēr'ē-ə-rāt')
v. de·te·ri·o·rat·ed, de·te·ri·o·rat·ing, de·te·ri·o·rates
To grow worse in function or condition.
To weaken or disintegrate.