Term in pro wrestling. Kayfabe was the unsaid rule that the wrestlers should stay in character during the show and in public appearences in order to maintain a feeling of reality (albeit suspended) among the fans
Wrestling term derived from "carnival talk" for the word "keep". Originally would have been pronounced more like "keel-feep". When said quickly, it sounds like kay-fabe. Used as shorthand term for "keep quiet", or "keep secret".
The word would not originally have been used as part of a sentence. It would have conveyed the meaning of a sentence in itself. The whole point of carnival talk was to speak quickly, and in manner that the "rubes" couldn't understand.