The Spirit of GR: Alpha-iota-theta-eta-rho

Book T says in one of the tables, referring to The Fool, "The Spirit of GR:Alpha-iota-theta-eta-rho"

I've been searching for a meaning of " GR: Alpha-iota-theta-eta-rho", but can't find anything. Maybe it's so obvious to most people that it doesn't need explanation anywhere.

Any help with this would be greatly appreciated ☺️