impenetrable


impenetrable (http://definr.com/impenetrable)

     adj 1: not admitting of penetration or passage into or through; "an
            impenetrable fortress"; "impenetrable rain forests"
            [ant: penetrable]
     2: permitting little if any light to pass through because of
        denseness of matter; "dense smoke"; "heavy fog";
        "impenetrable gloom" [syn: dense, heavy]
     3: impossible to understand; "impenetrable jargon"