@farah Herbert didn't explain it AFAIK. The Dune Encyclopedia mentions that it's a corruption of the word koranjiyana, but that was not written by Herbert so it might be the Encyclopedia's author idea. I guess it's one of those things that are basically left to the reader to figure out.
@farah Because the author wanted to show how religion is used to control people. And please understand that taking back that control was harder than it looked. Even rejection, they still leverage control.