The Collaborative International Dictionary of English v.0.48:

Stillness \Still"ness\, n.
   1. The quality or state of being still; quietness; silence;
      calmness; inactivity.
      [1913 Webster]

            Painting, then, was the art demanded by the modern
            intellect upon its emergence from the stillness of
            the Middle Ages.                      --J. A.
                                                  Symonds.
      [1913 Webster]

   2. Habitual silence or quiet; taciturnity.
      [1913 Webster]

            The gravity and stillness of your youth
            The world hath noted.                 --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

stillness
    n 1: (poetic) tranquil silence; "the still of the night" [syn:
         hush, stillness, still]
    2: calmness without winds [syn: stillness, windlessness]
    3: a state of no motion or movement; "the utter motionlessness
       of a marble statue" [syn: motionlessness, stillness,
       lifelessness] [ant: motion]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "stillness":
   ataraxia, ataraxy, awful silence, calmness, composure,
   contemplation, dead, dead of night, deathlike silence,
   golden silence, hush, hush of night, imperturbability,
   inaudibility, lucid stillness, lull, marmoreal repose, mum,
   nirvana, noiselessness, peace, peacefulness, placidity, placidness,
   quiescence, quiescency, quiet, quietism, quietness, quietude,
   repose, rest, restfulness, satori, serenity, silence, silentness,
   silken repose, sleep, slumber, solemn silence, soundlessness,
   still, tacitness, taciturnity, tomblike silence, tranquillity,
   whisht, wise passiveness