Source : Webster's Revised Unabridged Dictionary (1913)

Impermeable \Im*per"me*a*ble\, a. [Pref. im- not + permeable:
   cf. F. imperm['e]able, L. impermeabilis.]
   Not permeable; not permitting passage, as of a fluid. through
   its substance; impervious; impenetrable; as, India rubber is
   impermeable to water and to air. -- {Im*per"me*a*ble*ness},
   n. -- {Im*per"me*a*bly}, adv.

Source : WordNet®

impermeableness
     n : the property of something that cannot be pervaded by a
         liquid [syn: {impermeability}] [ant: {permeability}]