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

Moby Thesaurus II by Grady Ward, 1.0:

83 Moby Thesaurus words for "deadness":
   analgesia, anesthesia, aridity, barrenness, bloodlessness,
   callousness, characterlessness, colorlessness, dismalness,
   dragginess, dreariness, dryness, dullness, dustiness, effeteness,
   electronarcosis, emptiness, etiolation, flatness, flavorlessness,
   heaviness, hollowness, impassibility, imperception,
   imperceptiveness, imperceptivity, impercipience, inanity,
   inconsiderateness, inexcitability, insensibility, insensibleness,
   insensitiveness, insensitivity, insentience, insipidity,
   insipidness, jejuneness, jejunity, leadenness, lifelessness,
   lowness of spirit, mildness, muffled tone, mutedness, narcosis,
   narcotization, numbness, obtuseness, paleness, pallor,
   pins and needles, pointlessness, pokiness, ponderousness,
   saplessness, savorlessness, slowness, solemnity, spiritlessness,
   staleness, sterility, stiffness, stodginess, stuffiness,
   superficiality, tastelessness, tediousness, thick skin, thinness,
   unfeeling, unfeelingness, uninterestingness, unliveliness,
   unperceptiveness, unsavoriness, vapidity, vapidness, veiled voice,
   voce velata, weakness, wishy-washiness, woodenness