These words all refer to parts of a while, either integral or incidental. Addition and supplement share one sense in which the part and whole being joined are alike in kind, so that only an increase in quantity results.

• The new members will be a welcome addition to the club; A vitamin supplement is not necessary for the average diet.

Both words have uses, on the other hand, in which the part remains distinguishable from and subordinate to the whole.

• What a charming addition the sunroom makes to your house; The paper-covered book of quizzes was a supplement to the class’s mathematics textbook.

A supplement can also be a standard or special section of a newspaper: the Sunday supplement on the autumn fashions. Appendix , like supplement , can refer to a part of a book, but is more often bound with the book itself. Neither of these are essential to the book’s completeness, although both would offer additional details on given material.

Appendage refers to a more integral part of a whole than do any of the other terms. It is especially used in the life sciences to indicate the limbs or extremities of a plant or animal. No one except such a scientist, however, is likely ?even in the most formal of contexts ?to use appendage in preference to limb, branch, arm, leg, tail or whatever. Biologists themselves, in fact, can be every bit as exact and certainly more succinct in speaking of a monkey’s tail rather than its caudal appendage . In other uses of this word, the subordination of the part to the whole is emphasized. Such uses may be rather stiff except when a note of mockery is conveyed.

• It was apparent to everyone that the husband had become a mere appendage to his wealthy wife.

Appurtenance and adjunct both refer to a part that becomes a valuable addition to a whole, though not essential to it. Appurtenance has a specific legal sense of an incidental property right that goes together with a major right, such as the right of way to a building. The sense of a gratuitous advantage pervades its other meanings as well: He was unusual in considering her beauty as an appurtenance to her vigorous mind, and not vice versa. In adjunct, the separateness of the added part is stressed: Memorization is only an adjunct to real education, not its whole.

Attachment and accessory refer to parts that are neither essential to nor fused with the whole they complement. An attachment increases the usability of the original whole for which it is specifically designed, although its use is optional: If we had a flash-bulb attachment we could also take pictures at night. One meaning of accessory is identical with that of attachment , as in car accessories . Another sense of accessory points to its enhancing of the beauty, rather than the usefulness of the whole to which it is added: the tastefully chosen accessories that dramatize the simplest dress or suit.