appendix

American  

[uh-pen-diks] / əˈpɛn dɪks /

noun

appendices, plural appendixes plural

1. supplementary material at the end of a book, article, document, or other text, usually of an explanatory, statistical, or bibliographic nature.

   Synonyms:

   supplement, addition, appurtenance, adjunct, addendum

2. an appendage.

3. Anatomy.

   1. a process or projection.

   2. the vermiform appendix.

4. Aeronautics. the short tube at the bottom of a balloon bag, by which the intake and release of buoyant gas is controlled.

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appendix British  

/ əˈpɛndɪks /

noun

1. a body of separate additional material at the end of a book, magazine, etc, esp one that is documentary or explanatory

2. any part that is dependent or supplementary in nature or function; appendage

3. anatomy See vermiform appendix

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appendix Scientific  

/ ə-pĕn′dĭks /

appendixes plural

1. A tubular projection attached to the cecum of the large intestine and located on the lower right side of the abdomen.

2. Also called vermiform appendix

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appendix Cultural  

1. A small saclike organ located at the upper end of the large intestine. The appendix has no known function in present-day humans, but it may have played a role in the digestive system in humans of earlier times. The appendix is also called the vermiform appendix because of its wormlike (“vermiform”) shape.

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Spelling

Appendices, a plural borrowed directly from Latin, is the usual plural, especially in scholarly writing, when referring to supplementary material at the end of a book. Appendixes is the usual plural in the anatomical meaning.

Usage

Plural word for appendix The plural form of appendix can be either appendices, pronounced [ uh-pen-duh-seez ], or appendixes, but appendices is more widely used. The plural forms of several other singular nouns that end in -ix or -ex are also formed in this way, such as index/indices, matrix/matrices, and codex/codices.  Irregular plurals that are formed like appendices derive directly from their original pluralization in Latin. However, the standard English plural -es is often also acceptable for these terms, as in indexes and matrixes.

Synonym Usage

Appendix, supplement both mean material added at the end of a book. An appendix gives useful additional information, but even without it the rest of the book is complete: In the appendix are forty detailed charts. A supplement, bound in the book or published separately, is given for comparison, as an enhancement, to provide corrections, to present later information, and the like: A yearly supplement is issued.

Etymology

Origin of appendix

First recorded in 1535–45; from Latin: literally, “appendage,” equivalent to append(ere) “to add on” + -ix (equivalent to -ic- noun suffix + -s nominative singular ending); see origin at append

Explanation

No, it's not just a tiny organ pouch that requires surgery when it begins to hurt; an appendix is also additional material at the end of a book or paper. You would think that the appendix at the end of a book came after appendix the body part, wouldn't you? After all, our bodies have been around a lot longer than books have. But you'd be wrong. The name for the organ, also known as vermiform appendix, came into use later, no doubt because it is something attached — as its Latin root is translated — to the intestines just as an appendix is attached to the end of a book.

Example Sentences

A case study released alongside the global assessment identifies 20 migratory fish species in the Amazon that meet the criteria for potential CMS Appendix II listing.

From Science Daily • Mar. 26, 2026

One eel species, Anguilla anguilla, or the European eel, is considered critically endangered and was added to Appendix II in 2009.

From Barron's • Nov. 24, 2025

Appendix removal, however, seemed to be protective, which is something that other scientists have recognised before.

From BBC • Aug. 24, 2023

It placed them under Appendix II of the treaty, which means countries can no longer export them unless they certify that it won’t hurt shark sustainability.

From National Geographic • Jul. 17, 2023

Nixon and his wife, Pat, attended the White House church services with 125 guests, their names carefully listed in Appendix A in the Daily Diary.

From "Boots on the Ground: America's War in Vietnam" by Elizabeth Partridge

Related Words

• addendum
• postscript