The Collaborative International Dictionary of English v.0.48:

Monogamy \Mo*nog"a*my\, n. [L. monogamia, Gr. ?: cf. F.
   monogamie.]
   1. Single marriage; marriage with but one person, husband or
      wife, at the same time; -- opposed to polygamy. Also,
      one marriage only during life; -- opposed to
      deuterogamy.
      [1913 Webster]

   2. (Zool.) State of being paired with a single mate.
      [1913 Webster]

WordNet (r) 3.0 (2006):

monogamy
    n 1: having only one spouse at a time [syn: monogamy,
         monogamousness]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "monogamy":
   beena marriage, bigamy, common-law marriage, companionate marriage,
   concubinage, deuterogamy, left-handed marriage, levirate,
   leviration, love match, marriage of convenience, monandry,
   monogyny, morganatic marriage, picture marriage, polyandry,
   polygamy, polygyny, trial marriage, trigamy



Bouvier's Law Dictionary, Revised 6th Ed (1856):

MONOGAMY. A marriage contracted between one man and one woman, in exclusion
of all the rest of mankind; it is used in opposition to bigamy and polygamy.
(q.v.) Wolff, Dr. de la Nat. Sec. 857. The state of having only one husband
or one wife at one time.