non-starter

non- +‎ starter

non-starter (plural non-starters)

1. Someone or something who was listed to start in a race, but did not start in the race.
2. Something that is destined to fail from the outset; an impractical scheme.
   • 2020 December 2, Industry Insider, “The costs of cutting carbon”, in Rail, page 76:

     Whatever is decided, it is clear that Crossrail 2 must be regarded as a non-starter for the foreseeable future.

3. An idea or argument that cannot be sensibly debated.

• no go