Emily Dickinson Lexicon

AP-PEND'IX, n. [plur. Appendixes. L. The Latin plural is Appendices. See Append.]

1. Something appended or added. Normandy became an appendix to England. – Hale.
2. An adjunct, concomitant, or appendage. – Watts.
3. More generally, a supplement or short treatise added to a book.