Stillness, n.
1. The quality or state of being still; quietness; silence; calmness; inactivity. Painting, then, was the art demanded by the modern intellect upon its emergence from the stillness of the Middle Ages. J. A. Symonds.
2. Habitual silence or quiet; taciturnity. The gravity and stillness of your youth The world hath noted. Shak.
Shades of meaning
Fernald has no entry of its own for stillness; he lists it under apathy, rest.
He lists it without comment; the entries above explain its neighbors.