Source : Webster's Revised Unabridged Dictionary (1913)

Sedate \Se*date"\, a. [L. sedatus, p. p. of sedare, sedatum, to
   allay, calm, causative of sedere to sit. See {Sit}.]
   Undisturbed by passion or caprice; calm; tranquil; serene;
   not passionate or giddy; composed; staid; as, a sedate soul,
   mind, or temper.

         Disputation carries away the mind from that calm and
         sedate temper which is so necessary to contemplate
         truth.                                   --I. Watts.

         Whatsoever we feel and know Too sedate for outward
         show.                                    --Wordsworth.

   Syn: Settled; composed; calm; quiet; tranquil; still; serene;
        unruffled; undisturbed; contemplative; sober; serious.
        -- {Se*date"ly}, adv. -- {Se*date"ness}, n.

Source : WordNet®

sedateness
     n : a trait of dignified seriousness [syn: {staidness}, {solemnity},
          {solemness}]