polygamy

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The condition or practice of having more than one spouse at one time. Also called plural marriage.
2. n. Zoology A mating pattern in which a single individual mates with more than one individual of the opposite sex.

Century Dictionary and Cyclopedia

1. n. Marriage with more than one spouse; the having of a plurality of wives or husbands at the same time. In Christian countries, when a man has more wives than one, or a woman more husbands than one, at the same time, he or she is punishable for polygamy; but if there was a separate marriage with each the first marriage would be valid notwithstanding the subsequent ones, and the later ones would be void. The offense of contracting the subsequent marriage is now termed bigamy. But polygamy in the form of polygyny is allowed in some countries, especially among Mohammedans, and is held a matter of faith and duty by the Mormons. Compare polyandry.
2. n. In zoology, the practice or habit of having more than one mate of the opposite sex; polyandry or polygyny In mammals, polygamy is the rule with pinniped and various other carnivorous quadrupeds, with the hoofed quadrupeds in general, and in many other groups, especially in its polygynous form. In the class of birds, where monogamy is the rule, polygamy is conspicuous in the rasorial or gallinaceous order, and is exceptionally witnessed in some members of the monogamous orders, as in the cowbirds and cuckoos among passerine and picarian birds.

Wiktionary

1. n. The having of multiple socially bonded sexual partners at the same time
2. n. Commonly used specifically for polygyny, the marriage of a man to more than one wife, or the practice of having several wives, at the same time.
3. n. zoology The state or habit of having more than one sexual mate.
4. n. botany The condition or state of a plant which bears both perfect and unisexual flowers.

GNU Webster's 1913

1. n. 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. See the Note under bigamy, and cf. polyandry.
2. n. (Zoöl.) The state or habit of having more than one mate.
3. n. (Bot.) The condition or state of a plant which bears both perfect and unisexual flowers.

WordNet 3.0

1. n. having more than one spouse at a time