- leakproof, watertight - having no leaks
Antonym: unseaworthy (indirect, via seaworthy)
- watertight - not allowing water to pass in or out
Antonym: leaky (indirect, via tight)
- ironclad, unassailable, unshakable, watertight, bulletproof - without flaws or loopholes; "an ironclad contract"; "a watertight alibi"; "a bulletproof argument"
Antonym: contestable (indirect, via incontestable)