The Collaborative International Dictionary of English v.0.48:

Deaden \Dead"en\ (d[e^]d"'n), v. t. [imp. & p. p. Deadened
   (d[e^]d"'nd); p. pr. & vb. n. Deadening.] [From Dead; cf.
   AS. d?dan to kill, put to death. See Dead, a.]
   1. To make as dead; to impair in vigor, force, activity, or
      sensation; to lessen the force or acuteness of; to blunt;
      as, to deaden the natural powers or feelings; to deaden a
      sound.
      [1913 Webster]

            As harper lays his open palm
            Upon his harp, to deaden its vibrations.
                                                  --Longfellow.
      [1913 Webster]

   2. To lessen the velocity or momentum of; to retard; as, to
      deaden a ship's headway.
      [1913 Webster]

   3. To make vapid or spiritless; as, to deaden wine.
      [1913 Webster]

   4. To deprive of gloss or brilliancy; to obscure; as, to
      deaden gilding by a coat of size.
      [1913 Webster]

   5. To render impervious to sound, as a wall or floor; to
      deafen.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

deadened
    adj 1: devoid of physical sensation; numb; "his gums were dead
           from the novocain"; "she felt no discomfort as the
           dentist drilled her deadened tooth"; "a public
           desensitized by continuous television coverage of
           atrocities" [syn: dead, deadened]
    2: made or become less intense; "the deadened pangs of hunger"