The Collaborative International Dictionary of English v.0.48:

Solemnize \Sol"em*nize\, v. t. [imp. & p. p. Solemnized; p.
   pr. & vb. n. Solemnizing.] [Cf. F. solemniser,
   sollemniser.]
   1. To perform with solemn or ritual ceremonies, or according
      to legal forms.
      [1913 Webster]

            Baptism to be administered in one place, and
            marriage solemnized in another.       --Hooker.
      [1913 Webster]

   2. To dignify or honor by ceremonies; to celebrate.
      [1913 Webster]

            Their choice nobility and flowers . . .
            Met from all parts to solemnize this feast.
                                                  --Milton.
      [1913 Webster]

   3. To make grave, serious, and reverential.
      [1913 Webster]

            Wordsworth was solemnizzed and elevated by this his
            first look on Yarrow.                 --J. C.
                                                  Shairp.
      [1913 Webster]

            Every Israelite . . . arose, solemnized his face,
            looked towards Jerusalem . . . and prayed. --L.
                                                  Wallace.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Solemnize \Sol"em*nize\, n.
   Solemnization. [R.]
   [1913 Webster]

         Though spoused, yet wanting wedlock's solemnize.
                                                  --Spenser.
   [1913 Webster]

WordNet (r) 3.0 (2006):

solemnize
    v 1: observe or perform with dignity or gravity; "The King
         solemnized this day of morning" [syn: solemnize,
         solemnise]
    2: perform (the wedding ceremony) with proper ceremonies [syn:
       solemnize, solemnise]
    3: make solemn and grave; "This ceremony solemnized our hearts"
       [syn: solemnize, solemnise]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "solemnize":
   administer Communion, attend Communion, attend Mass, beat the drum,
   blow the trumpet, celebrate, celebrate Mass, commemorate,
   communicate, conventionalize, dignify, dress ship, fire a salute,
   formalize, freer, hallow, hold jubilee, honor, jubilate, jubilize,
   keep, maffick, make merry, mark, memorialize, observe,
   receive the Sacrament, ritualize, signalize, solemnly mark,
   sound a fanfare, stylize, venerate