watertight
[adjective]
Synonyms:
- waterproof
- foolproof, airtight, flawless, impregnable, sound, unassailable

[TahlilGaran] English Synonym Dictionary ▲

wa‧ter‧tight /ˈwɔːtətaɪt $ ˈwɒːtər-, ˈwɑː-/ adjective

1. a watertight container, roof, door etc does not allow water to get in or out ⇒ airtight

2. an argument, plan etc that is watertight is made very carefully so that people cannot find any mistakes in it:
Lucky for him, his alibi is watertight.
Unless the ban is watertight, EU laws will overturn it.

[TahlilGaran] Dictionary of Contemporary English ▲