万无一失

wàn wú yī shī

foolproof; absolutely safe

Character by character

万wàn
ten-thousand

无wú
without

一yī
one

失shī
slip

出发前再检查一遍，确保万无一失。

Check once more before we leave, so nothing can go wrong.

Tone: neutral.

Usually 确保／保证万无一失.

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