without flaws or loopholes; "an ironclad contract"; "a watertight alibi"; "a bulletproof argument"欠点も抜け穴もなしで要害堅固
immune to attack; incapable of being tampered with; "an impregnable fortress"; "fortifications that made the frontier inviolable"; "a secure telephone connection"攻撃に対しての免疫がある頑強