Source : Webster's Revised Unabridged Dictionary (1913)

Impenetrability \Im*pen`e*tra*bil"i*ty\, n. [Cf. F.
   imp['e]n['e]trabilit['e].]
   1. Quality of being impenetrable.

   2. (Physics) That property in virtue of which two portions of
      matter can not at the same time occupy the same portion of
      space.

   3. Insusceptibility of intellectual or emotional impression;
      obtuseness; stupidity; coldness.

Source : WordNet®

impenetrability
     n 1: resistance to penetration by a liquid [syn: {imperviousness}]
          [ant: {penetrability}, {penetrability}]
     2: incomprehensibility by virtue of being too dense to
        understand [syn: {impenetrableness}]