standby

We kept a battery-powered radio as a standby in case the electricity went out during the hurricane.

(Chinese) 我们备有一个电池供电的收音机，以防飓风期间停电。

The flight was fully booked, so I had to wait at the airport as a standby passenger for the next flight.

(Chinese) 航班已订满，所以我只能作为候补乘客在机场等待下一班飞机。