Source : Webster's Revised Unabridged Dictionary (1913)

Deafen \Deaf"en\, v. t. [imp. & p. p. {Deafened}; p. pr. & vb.
   n. {Deafening}.] [From {Deaf}.]
   1. To make deaf; to deprive of the power of hearing; to
      render incapable of perceiving sounds distinctly.

            Deafened and stunned with their promiscuous cries.
                                                  --Addison.

   2. (Arch.) To render impervious to sound, as a partition or
      floor, by filling the space within with mortar, by lining
      with paper, etc.

Source : WordNet®

deafened
     adj : caused to hear poorly or not at all