Something that is watertight does not allow water to pass through it, for example because it is tightly sealed.
例句
The flask is completely watertight, even when laid on its side...即使平放，这个真空水杯也是滴水不漏。The batteries are safely enclosed in a watertight compartment.电池被安全地置于一个防水的隔间里。
ADJ-GRADED
(事实、论点或协议)严密的，无懈可击的
A watertight case, argument, or agreement is one that has been so carefully put together that nobody will be able to find a fault in it.
例句
The police had a watertight case. They even got his fingerprints from that glass cabinet.警方找到了确凿的证据。他们甚至在那个玻璃橱柜上提取到了他的指纹。...a legally watertight agreement.严密规范的协议