Hey, stupid -- why not (imagine this) just Tass? Avoids that whole "but it describes this part of me but not others" thing by not really attempting to describe anything at all. Association of "repository of magic essence" works in a number of contexts. Sounds normal as anything else does on them internets. Concise, easy to pronounce, easy to spell. Doesn't really sound like any other words when spoken (Madyn sounds like "madden", Sterenn* like "staring"...), except maybe Taz (although I suppose I can deal with that - do I go BLARBAGRABLALLABLBO!! or am I a temporary autonomous zone? heheh). Has enough "cool factor" for me.
* -- Breton for "star".
mal_akh, I tried your suggestion, but apparently "star" itself goes back to Sanskrit (meaning something like "expanding in rays") and in most IE languages the word sounds pretty similar to that. Couldn't find anything else I liked (thought of trying "starlight", "galaxy" etc but couldn't think of words I really wanted to try translating!), although I did run across some interesting etymological dictionaries and stuff.
(why you bury me in the col', col' ground?)
* -- Breton for "star".
(why you bury me in the col', col' ground?)