Definition of "impregnable" []

• Impossible to capture or enter by force: an impregnable fortress. (adjective)
• Difficult or impossible to attack, challenge, or refute with success: an impregnable argument. (adjective)
• Capable of being impregnated. (adjective)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Charleston is a strongly fortified place and I think impregnable from the water side."
• "Given the regular news reports of enterprise data lost through laptop theft, third party misfeasance, WEP hacking, loss of backup tapes, disgruntled employees, etc., it’s not like enterprise data is currently held in impregnable Kryptonite fortresses."
• "It was this land side, containing the citadel and other works, which so impressed outsiders with the idea of impregnable strength."