Appendage, appurtenance, accessory and adjunct designate something regarded as additional and at the same time as subsidiary to another object.
Appendage implies a certain closeness of attachment or connection yet often stresses the idea of subordination or even uselessness.
- the caudal appendage
- the smaller borough is a mere appendage of the larger
- those graceful and useless appendages, called Directors
—Scott
Appurtenance is applied to something that belongs to the principal object or goes with it customarily yet is not an integral part of it (as the barns, worksheds, garages, gardens on a piece of land or the permanent fixtures in a building).
- the bed itself, with all appurtenances of palliasse, mattresses, etc.
—Barham
Accessory is applied usually to something that is dispensable yet contributes to the appearance, usefulness, comfort, or convenience of the principal thing.
- automobile accessories
- wore a beige suit with brown purse, gloves, and other accessories
Adjunct is applied to something that is or may be added or joined to the principal thing without becoming an essential part of it.
- in the great age of Louis XIV, it [the ballet] became an established institution, still an adjunct of opera
—Ellis - meter and rhyme are not mere adjuncts of poetry
—Alexander