impenetrable
adjective
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
Similar word(s): thick, dense, heavy
3. impossible to understand
- impenetrable jargon
Similar word(s): incomprehensible, uncomprehensible
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.