Source : Webster's Revised Unabridged Dictionary (1913)

Imperviable \Im*per"vi*a*ble\, a.
   Not pervious; impervious. [R.] -- {Im*per"vi*a*ble*ness}, n.
   [R.]

Source : WordNet®

imperviable
     adj : not admitting of passage or capable of being affected; "a
           material impervious to water"; "someone impervious to
           argument" [syn: {impervious}] [ant: {pervious}]