watertight

Adjective
  1. Not allowing water to pass in or out (synset 301402239)
    similar to: tight - of such close construction as to be impermeable
  2. 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, unassailable, unshakable

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