Most often I see control-U used as the "kill" character. This is the "line kill" behavior, not the "job kill" behavior that is more often used, as with "kill %1", or the similar process signal kill.
To reset it, use the literal 4 characters, '^u', then look at the assignment with stty -a again:
stty kill '^u'
I am not certain that this will work in an xterm
session, but give it a try and let us know. (In my xterm, stty reported the change, but it did not actually change the behavior. Perhaps someone will stop by with the usually-simple explanation
. It will likely be some arcane command or setting in an X configuration file.)
I have not seen this character assignment to kill in a long time; it once was the default with (real) TTYs.
Best wishes ... cheers, makyo