Source : Webster's Revised Unabridged Dictionary (1913)

Compressibility \Com*press`i*bil"i*ty\, n. [Cf. F.
   compressibilit['e].]
   The quality of being compressible of being compressible; as,
   the compressibility of elastic fluids.

Source : WordNet®

compressibility
     n : the property of being able to occupy less space [syn: {squeezability},
          {sponginess}] [ant: {incompressibility}]