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]