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

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "matrimony":
   a world-without-end bargain, alliance, baptism, bed,
   bond of matrimony, bridebed, cohabitation, confirmation,
   conjugal bond, conjugal knot, coverture, extreme unction,
   holy matrimony, holy orders, holy wedlock, husbandhood,
   ill-assorted marriage, intermarriage, interracial marriage,
   marriage, marriage bed, marriage sacrament, match,
   matrimonial union, mesalliance, misalliance, miscegenation,
   mixed marriage, nuptial bond, penance, sacrament of matrimony,
   seven sacraments, spousehood, the Eucharist, union, wedded bliss,
   wedded state, weddedness, wedding knot, wedlock, wifehood