The Collaborative International Dictionary of English v.0.48:

Decimate \Dec"i*mate\, v. t. [imp. & p. p. Decimated; p. pr. &
   vb. n. Decimating.] [L. decimatus, p. p. of decimare to
   decimate (in senses 1 & 2), fr. decimus tenth. See
   Decimal.]
   1. To take the tenth part of; to tithe. --Johnson.
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   2. To select by lot and punish with death every tenth man of;
      as, to decimate a regiment as a punishment for mutiny.
      --Macaulay.
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   3. To destroy a considerable part of; as, to decimate an army
      in battle; to decimate a people by disease.
      [1913 Webster]