万一

There is a supplementary water supply in case the rain supply fails.

万一主源断了, 我们另外有供方。

Although the sun was shining,I took an umbrella to be on the safe side.

虽然有太阳,但我仍带了伞以防万一。

I took the precaution of locking money in the safe.

我把所有钱都锁在保险箱里以防万一。

What if he's your rhumba boy?

万一他就是你伦巴男孩呢？

When the frequency changer has malfunction, power frequency is adopted, and the motor speed is nonadjustable.

万一变频器出现故障时，可工频驱动，转速不可调。

There will also be an 'underboss' who can run things should the 'boss' get thrown in the 'slammer'.

“头目”万一被抓进“班房”,这里还有一“头目”来打事情。