The Collaborative International Dictionary of English v.0.48:

Deadness \Dead"ness\, n.
   The state of being destitute of life, vigor, spirit,
   activity, etc.; dullness; inertness; languor; coldness;
   vapidness; indifference; as, the deadness of a limb, a body,
   or a tree; the deadness of an eye; deadness of the
   affections; the deadness of beer or cider; deadness to the
   world, and the like.
   [1913 Webster]

WordNet (r) 3.0 (2006):

deadness
    n 1: the quality of being unresponsive; not reacting; as a
         quality of people, it is marked by a failure to respond
         quickly or with emotion to people or events; "she began to
         recover from her numb unresponsiveness after the accident";
         "in an instant all the deadness and withdrawal were wiped
         away" [syn: unresponsiveness, deadness] [ant:
         responsiveness]
    2: the physical property of something that has lost its
       elasticity; "he objected to the deadness of the tennis balls"
    3: the inanimate property of something that has died