N-SING
(尤指航天器发射前的)倒计时
A countdown is the counting aloud of numbers in reverse order before something happens, especially before a spacecraft is launched.
例句
The countdown has begun for the launch later today of the American space shuttle...
美国航天飞机的发射已于今天晚些时候开始进入倒计时。
There were three more things to do before countdown.
开始倒计时之前还有3件事要做。