Source : Webster's Revised Unabridged Dictionary (1913)

Hollowness \Hol"low*ness\, n.
   1. State of being hollow. --Bacon.

   2. Insincerity; unsoundness; treachery. --South.

Source : WordNet®

hollowness
     n 1: the state of being hollow: having an empty space within
          [ant: {solidity}]
     2: the property of having a sunken area