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]