watertight
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.
wa‧ter‧tight /ˈwɔːtətaɪt $ ˈwɒːtər-, ˈwɑː-/
adjective1. 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: