a one in a million chance

a one-in-a-million chance

A very slim chance. He's got a one in a million chance of making that putt—I doubt the ball goes in.
See also: chance
Farlex Dictionary of Idioms.

a one in a million chance

or

a chance in a million

If you say that something is a one in a million chance or that there is a chance in a million of it happening, you mean that it is very unlikely to happen, and that you would be either extremely lucky or extremely unlucky if it happened to you. Now we're hoping and praying for another organ donor. It has to be a perfect match and there's all the waiting for that one in a million chance. Macleod said he entered the competition believing he had a one-in-a-million chance of coming first. It is amazing really. He had a chance in a million of surviving
See also: chance, million, one
Collins COBUILD Idioms Dictionary, 3rd ed.
See also:
  • a one-in-a-million chance
  • one chance in a million
  • dog's chance
  • lose out
  • lose out on (something)
  • lose out on
  • on the (off) chance
  • on the chance
  • miss out on
  • miss out on (something)