expression
just in case; as a precaution
Used when preparing for an unlikely but possible emergency or problem. Often appears with verbs like 用意する, 準備する, or 持っていく.
万一のために傘を持っていく。
I'll take an umbrella just in case.
万一のためにお金を少し多めに用意した。
I prepared a little extra money just in case.