What is the origin of the word "kayfabe"?

Not the concept, the word itself. I know a lot of wrestling terms have carny slang origins, but most of them are real words or combinations of words where the meaning or origin is fairly clear. "Work", "face", "pop", etc.

"Kayfabe" doesn't seem to have any connection to any word in the English language far as I can tell, and the few articles online I've seen don't really go into it or just offer conflicting or speculative theories. Have any linguists or historians actually looked into this and found anything solid?