Webster's English Dictionary

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impervious

im.per.vi.ous \(')im-'p*r-ve--*s\ aj [L impervius, fr. in- + pervius 
   pervious] 1: not allowing entrance or passage : IMPENETRABLE {a coat ~)R to 
   rain} 2: not capable of being affected or disturbed {~ to criticism}  - 
   im.per.vi.ous.ly av