unassailable

Adjective
  1. Immune to attack;
    Incapable of being tampered with (synset 302536283)
    "an impregnable fortress"; "fortifications that made the frontier inviolable"; "a secure telephone connection"
    similar to: invulnerable - immune to attack; impregnable
    same as: impregnable, inviolable, secure, strong, unattackable
  2. Impossible to assail (synset 302520844)
    similar to: inviolable - incapable of being transgressed or dishonored
    same as: untouchable
  3. Without flaws or loopholes (synset 300594206)
    "an ironclad contract"; "a watertight alibi"; "a bulletproof argument"
    similar to: incontestable, incontestible - incapable of being contested or disputed
    same as: bulletproof, unshakable, watertight

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