Scotch mist

noun5

1. •
   (UK) A cold and penetrating mist, verging on rain.
2. •
   (dialect, UK) Something that is hard to find or does not exist.

   • Scotch mist, the R.A.F. term for something imaginary. […] The joke of it is that Scotch mist is as wetting as English rain. — 1945
3. •
   (dialect, UK) Something imaginary, nonexistent, or overlooked.
4. •
   A drink of Scotch whisky served with ice and lemon peel.
5. •
   The perennial flowering plant Galium sylvaticum.