I remember hearing toon over a decade ago, but it was definitely a "controversial" term back then. I never really liked it myself because it never made sense to me. Character and avatar are good.
It took me a while to start calling servers servers instead of "shards" because that's what they were called in Ultima Online for lore reasons. I've seen some newer MMORPGs use the term, but it's pretty rare. I think some tech people use the term for similar stuff, too.