1. spoil; decline; become worse. deterioratede*teri*o*rate (d&esl;*tēr&ibreve;*&osl;*rāt), v. t. [imp. & p. p. deteriorated (-rā`t&ebreve;d); p. pr. & vb. n. deteriorating (-rā`t&ibreve;ng).] [l. deterioratus, p. p. of deteriorare to deteriorate, fr. deterior worse, prob. a comparative fr. de down, away.] to make worse; to make inferior in quality or value; to impair; as, to deteriorate the mind. the art of war was greatly deteriorated.deteriorate de*teri*o*rate (d&esl;*tēr&ibreve;*&osl;*rāt), v. i. to grow worse; to be impaired in quality; to degenerate. under such conditions, the mind rapidly deteriorates.deteriorate v