LOL!!!!...by a loooong stretch of etymologocal license!
Here's the OED approach:
Bu-cetum (Latin)=> kait- (teutonic root) => haihi (Goth) => haide (Middle
German ) => haeacu (Old English) => heath (English).
...maybe our OED editor got his inspiration by ingesting Creutzfeld-Jacobs-laced kidney pudding...