The name's two-fold.
Firstly it's from an old cartoon in one of the Molesworth books by Geoffrey Willans and Ronal Searle (who also drew the St.Trinians cartoons).
A schoolmaster is screaming at a 7 year old child who has mistranslated some Latin "No! 'The spirit of tolerance' You fool!"
Secondly, I love reading Iain M. Banks Science Fiction Novels, and the sentient space ships always give themselves highly inappropriate names that are the exact opposite of their nature.
Hence "The Spirit Of Tolerance".
My other Eldar names are usually titles or lines from songs.