Wordnet 3.0
ADJECTIVE (1)
1. 
 not admitting of passage or capable of being affected; 
- Example: "a material impervious to water"- Example: "someone impervious to argument"[syn: impervious, imperviable]
The Collaborative International Dictionary of English v.0.48:
Imperviable \Im*per"vi*a*ble\, a.
   Not pervious; impervious. [R.] -- Im*per"vi*a*ble*ness, n.
   [R.]
   [1913 Webster]
WordNet (r) 3.0 (2006):
imperviable
    adj 1: not admitting of passage or capable of being affected; "a
           material impervious to water"; "someone impervious to
           argument" [syn: impervious, imperviable] [ant:
           pervious]