Definition of "impenetrable" in English

adjective

1. Not penetrable.

   • The fortress is impenetrable, so it cannot be taken.

2. Opaque; obscure; not translucent or transparent.

3. (figuratively) Incomprehensible; fathomless; inscrutable.

   • Business jargon makes this document impenetrable—I can’t understand it.

noun

1. A person not openly given to friendship.