资料来源 : Webster's Revised Unabridged Dictionary (1913)

Impenetrableness \Im*pen"e*tra*ble*ness\, n.
   The quality of being impenetrable; impenetrability.

资料来源 : WordNet®

impenetrableness
     n : incomprehensibility by virtue of being too dense to
         understand [syn: {impenetrability}]