Source : Webster's Revised Unabridged Dictionary (1913)

Unsound \Un*sound"\, a.
   Not sound; not whole; not solid; defective; infirm; diseased.
   -- {Un*sound"ly}, adv. -- {Un*sound"ness}, n.

Source : WordNet®

unsoundness
     n : a condition of damage or decay [ant: {soundness}]