What a rigamarole.
First I quit the account (and can never go back - but oh, wait, I could if I changed my screen name).
Then I looked again at my Applications and saw three gimps in there, that weren't there the three times I looked before. Trashed them.
Then I tossed the Gimp icon in the trash but the trash refused it, and refused it again. A notice said I should quit applications.
But there were no items of this date in applications.
Tried closing that, no dice re it helping me trash the icon.
Finally shut off the mac, turned it on again, and voila, I'm free of it.
Obviously, a huge part of all this is from my end, but I didn't find it user friendly. I guess it isn't supposed to be.
I'll rest a bit and then try to figure out the x11 business.
(adds, looks like x11 relates to ms windows, I think I'll let that go for now.)