The Collaborative International Dictionary of English v.0.48:

Matrimony \Mat"ri*mo*ny\, n. [OE. matrimoine, through Old
   French, fr. L. matrimonium, fr. mater mother. See Mother.]
   1. The union of man and woman as husband and wife; the
      nuptial state; marriage; wedlock.
      [1913 Webster]

            If either of you know any impediment, why ye may not
            be lawfully joined together in matrimony, ye do now
            confess it.                           --Book of Com.
                                                  Prayer (Eng.
                                                  Ed.)
      [1913 Webster]

   2. A kind of game at cards played by several persons.
      [1913 Webster]

   Matrimony vine (Bot.), a climbing thorny vine (Lycium
      barbarum) of the Potato family. --Gray.
      [1913 Webster]

   Syn: Marriage; wedlock. See Marriage.
        [1913 Webster]

WordNet (r) 3.0 (2006):

matrimony
    n 1: the state of being a married couple voluntarily joined for
         life (or until divorce); "a long and happy marriage"; "God
         bless this union" [syn: marriage, matrimony, union,
         spousal relationship, wedlock]
    2: the ceremony or sacrament of marriage