Synonyms: unassailable, bulletproof, unshakable, watertight
Definition: without flaws or loopholes
Usage: an ironclad contract; a watertight alibi; a bulletproof argument
Similar words: incontestable, incontestible
Definition: incapable of being contested or disputed
Synonyms: watertight
Definition: not allowing water to pass in or out
Similar words: tight
Definition: of such close construction as to be impermeable
Usage: a tight roof; warm in our tight little house