What does the word impenetrable mean?

Usage examples for impenetrable

  1. She turned away, weary of questioning the impenetrable future, and went back to the inn. – Man and Wife by Wilkie Collins
  2. France in control of Louisiana and Florida would be " a wall of brass forever impenetrable to the combined efforts of England and America." – Union and Democracy by Allen Johnson
  3. The impenetrable composure of that reply took Grace completely by surprise. – The New Magdalen by Wilkie Collins