I am asking about the reason for the use of this letter, if known, as well as the initial occasion of its use. Ideas that have been suggested concerning the former include:
- That it stands for geometry or Geometrie
- That it stands for some other German word
- That it is in homage to Gauss
- That it refers to Gravitation
- That it refers to the Gram matrix
As for the latter, I'm guessing it originates somewhere between Riemann and Einstein.