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" ;