The Collaborative International Dictionary of English v.0.48:

Solemnity \So*lem"ni*ty\, n.; pl. Solemnities. [L. solemnitas,
   solennitas: cf. F. solennit['e], solemnit['e], OF. also
   sollempnit['e].]
   1. A rite or ceremony performed with religious reverence;
      religious or ritual ceremony; as, the solemnity of a
      funeral, a sacrament.
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            Great was the cause; our old solemnities
            From no blind zeal or fond tradition rise,
            But saved from death, our Argives yearly pay
            These grateful honors to the god of day. --Pope.
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   2. ceremony adapted to impress with awe.
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            The forms and solemnities of the last judgment.
                                                  --Atterburry.
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   3. Ceremoniousness; impressiveness; seriousness; grave
      earnestness; formal dignity; gravity.
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            With much glory and great solemnity.  --Chaucer.
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            The statelines and gravity of the Spaniards shows
            itself in the solemnity of their language.
                                                  --Addison.
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            These promises were often made with great solemnity
            and confirmed with an oath.           --J. Edwards.
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   4. Hence, affected gravity or seriousness.
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            Solemnity 's a cover for a sot.       --Young.
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   5. Solemn state or feeling; awe or reverence; also, that
      which produces such a feeling; as, the solemnity of an
      audience; the solemnity of Westminster Abbey.
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   6. (Law) A solemn or formal observance; proceeding according
      to due form; the formality which is necessary to render a
      thing done valid.
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WordNet (r) 3.0 (2006):

solemnity
    n 1: a trait of dignified seriousness [syn: sedateness,
         staidness, solemnity, solemness]
    2: a solemn and dignified feeling [syn: gravity, solemnity]
       [ant: levity]