The Collaborative International Dictionary of English v.0.48:

Depopulate \De*pop"u*late\, v. t. [imp. & p. p. Depopulated;
   p. pr. & vb. n. Depopulating.] [L. depopulatus, p. p. of
   depopulari to ravage; de- + populari to ravage, fr. populus
   people: cf. OF. depopuler, F. d['e]peupler. See People.]
   To deprive of inhabitants, whether by death or by expulsion;
   to reduce greatly the populousness of; to dispeople; to
   unpeople.
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         Where is this viper,
         That would depopulate the city?          --Shak.
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   Note: It is not synonymous with laying waste or destroying,
         being limited to the loss of inhabitants; as, an army
         or a famine may depopulate a country. It rarely
         expresses an entire loss of inhabitants, but often a
         great diminution of their numbers; as, the deluge
         depopulated the earth.
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The Collaborative International Dictionary of English v.0.48:

Depopulate \De*pop"u*late\, v. i.
   To become dispeopled. [R.]
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         Whether the country be depopulating or not.
                                                  --Goldsmith.
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WordNet (r) 3.0 (2006):

depopulate
    v 1: reduce in population; "The epidemic depopulated the
         countryside" [syn: depopulate, desolate]