expression, noun which may take the genitive case particle 'no'
one in a million; extremely unlikely
Used to describe a very slim chance or a highly improbable event. Often appears in conditional expressions like 万に一つも～ない or 万に一つの確率.
The chance of winning the lottery is not even one in a million.
I'll bet on that one-in-a-million possibility.
Kana spelling of 一つ; slightly softer or more explanatory in feel.
Literally 'one in ten thousand', from 万 (ten thousand) and 一つ (one). The number 万 is used hyperbolically to express an extremely small probability.