The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

         Disputation carries away the mind from that calm and
         sedate temper which is so necessary to contemplate
         truth.                                   --I. Watts.
   [1913 Webster]

         Whatsoever we feel and know
         Too sedate for outward show.             --Wordsworth.
   [1913 Webster]

   Syn: Settled; composed; calm; quiet; tranquil; still; serene;
        unruffled; undisturbed; contemplative; sober; serious.
        [1913 Webster] -- Se*date"ly, adv. -- Se*date"ness,
        n.
        [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

84 Moby Thesaurus words for "sedate":
   anesthetize, aristocratic, august, calm, collected, composed,
   controlled, conventional, cool, courtly, decorous, demure,
   detached, dignified, dispassionate, dope, drug, earnest, entrance,
   even-tempered, formal, frowning, fussy, grand, grave, grim,
   grim-faced, grim-visaged, hypnotize, imperturbable, imposing,
   kingly, long-faced, lordly, lull to sleep, magisterial, magnetize,
   majestic, mesmerize, moderate, narcotize, no-nonsense, noble,
   old-fashioned, peaceful, placid, prim, princely, proper, prudish,
   put to sleep, put under, queenly, refined, regal, rock to sleep,
   royal, seemly, serene, serious, sober, sober-minded, sobersided,
   solemn, somber, staid, stately, statuesque, stiff, stone-faced,
   straight-faced, strait-laced, temperate, thoughtful, trance,
   tranquil, undisturbed, unflappable, unperturbed, unruffled,
   unsmiling, venerable, weighty, worthy