1. appetizer, starter, hors d'oeuvre (small, light, and usually savory first course in a meal) (cooking)

2. extension, appurtenance (room of a building that is not part of the main structure) (architecture)

3. digression (act of straying from the main subject that could be removed from the text without detriment to the main plot) (literature)

4. addendum, extraneity, superfluity, accessory, hors-d'oeuvre (something additional or secondary to the main thing) (figurative, figuratively)