1. not admitting of penetration or passage into or through
- an impenetrable fortress
- impenetrable rain forests
2. permitting little if any light to pass through because of denseness of matter
- impenetrable gloom
3. impossible to understand
- impenetrable jargon
Sentences with impenetrable as an adjective:
- The fortress is impenetrable, so it cannot be taken.
- Business jargon makes this document impenetrable, I can't understand it.