Main entry: impenetrable
Definition: impossible to understand
Usage: impenetrable jargon
Main entry: impenetrable
Definition: not admitting of penetration or passage into or through
Usage: an impenetrable fortress; impenetrable rain forests
Main entry: dense, impenetrable, heavy
Definition: permitting little if any light to pass through because of denseness of matter
Usage: dense smoke; heavy fog; impenetrable gloom