The Collaborative International Dictionary of English v.0.48:

Mixed \Mixed\, a.
   Formed by mixing; united; mingled; blended. See Mix, v. t.
   & i.
   [1913 Webster]

   Mixed action (Law), a suit combining the properties of a
      real and a personal action.

   Mixed angle, a mixtilineal angle.

   Mixed fabric, a textile fabric composed of two or more
      kinds of fiber, as a poplin.

   Mixed marriage, a marriage between persons of different
      races or religions; specifically, one between a Roman
      Catholic and a Protestant.

   Mixed number, a whole number and a fraction taken together.


   Mixed train, a railway train containing both passenger and
      freight cars.

   Mixed voices (Mus.), voices of both males and females
      united in the same performance.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mixed marriage
    n 1: marriage of two people from different races or different
         religions or different cultures; "the families of both
         partners in a mixed marriage often disapprove"

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "mixed marriage":
   a world-without-end bargain, alliance, bed, bond of matrimony,
   bridebed, cohabitation, conjugal bond, conjugal knot, coverture,
   holy matrimony, holy wedlock, husbandhood, ill-assorted marriage,
   intermarriage, interracial marriage, marriage, marriage bed,
   marriage sacrament, match, matrimonial union, matrimony,
   mesalliance, misalliance, miscegenation, nuptial bond,
   sacrament of matrimony, spousehood, union, wedded bliss,
   wedded state, weddedness, wedding knot, wedlock, wifehood