Also it is German for soul. The creator of Eva Hideaki Anno put so many references and symbolism into Neon Genesis Evangelion that I am still finding new things out all the time.

Update 19/04/01

A secret organization that existed since before Second Impact. It covered up the truth about Second Impact and the existence of the Angels, and possesses power exceeding even that of sovereign nations and the UN. After Second Impact, it used the UN as a front to establish the Instrumentality Committee and Special Agency NERV, and to build the Eva series. SEELE's Instrumentality Project proceeded according to the account written in the "Secret Dead Sea Scrolls", and aimed to move humankind to the next level of evolution. However, the loss of the Lance of Longinus and then the further rebellion of NERV Commander Gendou Ikari forced SEELE to modify the plan at the final stage. Incidentally, "Seele" means "soul" in German. Further, the names of all the organizations that are related to SEELE, such as GEHIRN and NERV, are also derived from German. Could it be that SEELE originated in Germany?

Source: The End of Evangelion : Glossary contained within The End of Evangelion - Theatrical Program.