万(まん)が一(いち)

まんがいち
adverb, noun
just in case; by any chance
quantity
1. just in case, by any chance
Used to express a very unlikely but possible scenario. Literally "one in ten thousand." Often paired with conditional forms (〜たら、〜ば) or the expression の場合(ばあい)は to describe precautionary measures or worst-case scenarios.
万(まん)が一(いち)に備(そな)える。
Prepare for the worst.
万(まん)が一(いち)のために保険(ほけん)に入(はい)った。
I got insurance just in case.
万(まん)が一(いち)火事(かじ)が起(お)きたら、この非常口(ひじょうぐち)から逃(に)げてください。
In the unlikely event of a fire, please escape through this emergency exit.

万(まん)が一(いち) literally means "one in ten thousand" and is used to talk about unlikely but possible events. It is more emphatic than もしも and carries a stronger sense of improbability.

Common collocations

Usage

  • Typically used with conditional patterns: 万(まん)が一(いち)〜たら / 〜ば
  • Often appears in formal warnings, safety instructions, and insurance contexts
  • Can function as a noun when followed by の: 万(まん)が一(いち)の時(とき)
general
Added 2026.2.15 9:17 · Revised 2026.9.4 21:29
17500/17693_mangaichi