What does the word impregnable mean?

Usage examples for impregnable

  1. Evan made an appeal to his reason, but finding that impregnable, he pulled out his scanty purse to guarantee his sincerity with an offer of pledgemoney. – The Complete Project Gutenberg Works of George Meredith by George Meredith
  2. With those two on guard, Appleboro knew its bank was as impregnable as Gibraltar. – Slippy McGee, Sometimes Known as the Butterfly Man by Marie Conway Oemler
  3. You must know that I held a high official position in the religious world- I will mention no details- and I found at an early age, I am glad to say, the imperative necessity of forming absolutely impregnable convictions. – The Child of the Dawn by Arthur Christopher Benson