Synonyms for appendage

These nouns denote subordinate elements added to another entity. An appendage supplements without being essential: “ … and the complete absence of appendages at the stern decreases hull resistance” (R.J.L. Dicker).
An appurtenance belongs naturally as a subsidiary attribute, part, or member: “an internationally known first-class hotel … equipped with such appurtenances as computers, word processors, copiers and telex” (Oscar Millard).
An adjunct is added as an auxiliary but is often self-sustaining: “Intelligence analysts … believe that of all the countries of the Middle East, none use terrorism more effectively as an adjunct to diplomacy …” (Elaine Sciolino).
An accessory is usually nonessential but desirable: Our new car has such accessories as air conditioning and a sunroof.
An attachment adds a function to the thing to which it is connected: The food processor has an attachment for kneading dough.