impenetrable Synonyms

heavy dense unfathomable impregnable tough thickened thick telestic supersensible sturdy trackless unaccessible unaccountable weatherproof wayless vitrified unsurmountable unsearchable unpenetrable unpassable unconquerable stony soupy solid pathless overgrown opaque occult obscure mystifying mystic mysterious perplexing plumbic protective sibylline serried secretive sealed safe resistant recondite puzzling mysterial wakeless rocklike rainproof unprocurable unapparent unclear