Source : Webster's Revised Unabridged Dictionary (1913)

Polygamy \Po*lyg"a*my\, n. [Gr. ?; cf. F. polygamie.]
   1. The having of a plurality of wives or husbands at the same
      time; usually, the marriage of a man to more than one
      woman, or the practice of having several wives, at the
      same time; -- opposed to monogamy; as, the nations of the
      East practiced polygamy. See the Note under {Bigamy}, and
      cf. {Polyandry}.

   2. (Zo["o]l.) The state or habit of having more than one
      mate.

   3. (Bot.) The condition or state of a plant which bears both
      perfect and unisexual flowers.

Source : WordNet®

polygamy
     n : having more than one spouse at a time