Source : Webster's Revised Unabridged Dictionary (1913)

Solemn \Sol"emn\, a. [OE. solempne, OF. solempne, L. solemnis,
   solennis, sollemnis, sollennis; sollus all, entire + annus a
   year; properly, that takes place every year; -- used
   especially of religious solemnities. Cf. {Silly}, {Annual}.]
   1. Marked with religious rites and pomps; enjoined by, or
      connected with, religion; sacred.

            His holy rites and solemn feasts profaned. --Milton.

            The worship of this image was advanced, and a solemn
            supplication observed everry year.    --Bp.
                                                  Stillingfleet.

   2. Pertaining to a festival; festive; festal. [Obs.] ``On
      this solemn day.'' --Chaucer.

   3. Stately; ceremonious; grand. [Archaic]

            His feast so solemn and so rich.      --Chaucer.

            To-night we hold a splemn supper.     --Shak.

   4. Fitted to awaken or express serious reflections; marked by
      seriousness; serious; grave; devout; as, a solemn promise;
      solemn earnestness.

            Nor wanting power to mitigate and swage With solemn
            touches troubled thoughts.            --Milton.

            There reigned a solemn silence over all. --Spenser.

   5. Real; earnest; downright. [Obs. & R.]

            Frederick, the emperor, . . . has spared no expense
            in strengthening this city; since which time we find
            no solemn taking it by the Turks.     --Fuller.

   6. Affectedly grave or serious; as, to put on a solemn face.
      ``A solemn coxcomb.'' --Swift.

   7. (Law) Made in form; ceremonious; as, solemn war;
      conforming with all legal requirements; as, probate in
      solemn form. --Burrill. --Jarman. --Greenleaf.

   {Solemn League and Covenant}. See {Covenant}, 2.

   Syn: Grave; formal; ritual; ceremonial; sober; serious;
        reverential; devotional; devout. See {Grave}.

Source : WordNet®

solemn
     adj 1: dignified and somber in manner or character and committed to
            keeping promises; "a grave God-fearing man"; "a quiet
            sedate nature"; "as sober as a judge"; "a solemn
            promise"; "the judge was solemn as he pronounced
            sentence" [syn: {grave}, {sedate}, {sober}]
     2: characterized by a firm and humorless belief in the validity
        of your opinions; "both sides were deeply in earnest, even
        passionate"; "an entirely sincere and cruel tyrant"; "a
        film with a solemn social message" [syn: {earnest}, {in
        earnest(p)}, {sincere}]