K
from Fancyclopedia 2 ca. 1959
Back in 1944 Speer could brush aside K as initialing no important fan words — "leave one letter of the alphabet temporarily unsullied by stfandom", was the way he put it. But in this harsh world fifteen years later nothing's sacred any more.
from Fancyclopedia 1 ca. 1944
No important fan words at present being initialed by K, it pleases our whimsy to brush aside one or two that mite have been stuck in, and leave one letter of the alphabet temporarily unsullied by stfandom.

Also: Apazine edited by Vince Clarke for Pieces of Eight. (1990-97)