Meaning of yǐ fáng wàn yī:
yǐ fáng wàn yī
以防万一
Conjunction
to guard against the unexpected (idiom); just in case; prepared for any eventualities
Wǒ zǒng shì dài sǎn chūmén, yǐ fáng wàn yī xiàyǔ.
我总是带伞出门,以防万一下雨。
I always take an umbrella when I go out, just in case it rains.
Wǒ dài le yī bǎ sǎn, yǐ fáng wàn yī jīntiān xiàyǔ.
我带了一把伞,以防万一今天下雨。
I brought an umbrella just in case it rains today.