Definition of "impenetrable" []

• Impossible to penetrate or enter: an impenetrable fortress. (adjective)
• Impossible to understand; incomprehensible: impenetrable jargon. (adjective)
• Impervious to sentiment or argument: an impenetrable heart. (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.

• "Announcing his response to a formal consultation, Cable outlined plans for greater diversity on boards – including requiring boards to contain two people who had never had seats in boardrooms before – and to make remuneration reports, which he described as "impenetrable", easier to understand."
• "It was not in impenetrable shadow as the other objects in the yard were, but had a dismal light about it, like a bad lobster in a dark cellar."
• "Even this strong man shrank from this idea and showed a very natural recoil as his glances flew about the ill-omened room and finally rested on the fireside over which so repellent a mystery hung in impenetrable shadow."