appetizer, starter, hors d'oeuvre (small, light, and usually savory first course in a meal); extension, appurtenance (room of a building that is not part of the main structure); digression (act of straying from the main subject that could be removed from the text without detriment to the main plot); addendum, extraneity, superfluity, accessory, hors-d'oeuvre (something additional or secondary to the main thing)