Adjective

• S: (adj) impenetrable (not admitting of penetration or passage into or through) "an impenetrable fortress"; "impenetrable rain forests"
• similar to
• antonym
• derivationally related form
• S: (adj) dense, heavy, impenetrable (permitting little if any light to pass through because of denseness of matter) "dense smoke"; "heavy fog"; "impenetrable gloom"
• S: (adj) impenetrable (impossible to understand) "impenetrable jargon"
• similar to
• derivationally related form
• antonym