"impenetrable" in the adjective sense
1. impenetrable
not admitting of penetration or passage into or through
"an impenetrable fortress"
"impenetrable rain forests"
2. dense, heavy, impenetrable
permitting little if any light to pass through because of denseness of matter
"dense smoke"
"heavy fog"
"impenetrable gloom"
3. impenetrable
impossible to understand
"impenetrable jargon"
Source: WordNet® (An amazing lexical database of English)
Princeton University "About WordNet®."
WordNet®. Princeton University. 2010.
View WordNet® License