(a.) Impenetrable; not capable being penetrated or affected; as, impervious to fear\.

Philistine airtight ballproof beyond reach bombproof bulletproof burglarproof callous calloused case-hardened closed forever to closed to corrosionproof dampproof fire-resisting fireproof flameproof flinty foolproof hard hardened hardhearted hermetic holeproof impassable impenetrable impermeable impersuadable impersuasible impervious to inaccessible indurated inflexible insensitive inured leakproof lost to noiseproof nonpuncturable obstinate out of reach pachydermatous proof proof against punctureproof resistant rustproof shatterproof shellproof soundproof steeled against steely stony thick-skinned tight un-come-at-able unaccessible unamenable unapproachable unattainable unavailable undiscoverable ungettable unimpressionable uninfluenceable unmovable unobtainable unpassable unperforable unpersuadable unpierceable unpliable unprocurable unreachable unreceptive unresponsive unsecurable unsuggestible unsusceptible unswayable unyielding watertight weatherproof