Deteriorate

De*te"ri*o*rate (dē*tē"rĭ*?*rāt), v. i. To grow worse; to be impaired in quality; to degenerate.

Under such conditions, the mind rapidly deteriorates.
Goldsmith.

De*te"ri*o*rate (dē*tē"rĭ*?*rāt), v. t. [imp. & p. p. Deteriorated (- rā`tĕd); p. pr. & vb. n. Deteriorating (-rā`tĭng).] [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. Whately.

The art of war . . . was greatly deteriorated.
Southey.