The Collaborative International Dictionary of English v.0.48:

Impoverish \Im*pov"er*ish\, v. t. [imp. & p. p. Impoverished;
   p. pr. & vb. n. Impoverishing.] [OF. empovrir; pref. em-
   (L. in) + povre poor, F. pauvre; cf. OF. apovrir, F.
   appauvrir, where the prefix is a-, L. ad. Cf. Empoverish,
   and see Poor, and -ish.]
   1. To make poor; to reduce to poverty or indigence; as,
      misfortune and disease impoverish families.
      [1913 Webster]

   2. To exhaust the strength, richness, or fertility of; to
      make sterile; as, to impoverish land.
      [1913 Webster]