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.

Other Word Forms

Noun Inflected Forms

• appendices
  plural
• appendixes
  plural

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

See Examples For:

appendix appendices appendixes

By then, doctors had removed her appendix, mistakenly thinking she had acute appendicitis.

From BBC ● Jul. 19, 2026

The appendix, once considered a completely useless evolutionary left-over, is now thought to have minor immune functions.

From Science Daily ● Jul. 11, 2026

Some of the most illuminating material in “Defending Taiwan” arrives in an appendix, where the author interviews four prominent figures in Taipei.

From The Wall Street Journal ● May 14, 2026

When he was 12, his appendix ruptured and he nearly died, leading him to promise to serve God as an adult.

From Los Angeles Times ● Jan. 31, 2026

It means that your appendix, which is about the size of your tongue, and located right here, she says, pointing to the bottom of her stomach on the right side, has ruptured.

From "Booked" by Kwame Alexander

The U.S. blueprint has been spelled out in appendices to current peace proposals that aren’t public but were described to The Wall Street Journal by U.S. and European officials.

From The Wall Street Journal ● Dec. 10, 2025

But following appeals lodged by industry groups, the ICC board moved the measures to the code’s appendices, effectively making them optional, as first reported by the HuffPost.

From Seattle Times ● Apr. 14, 2024

Lynda Claassen: Have you thought about, or have you found out anything about the publication of my appendices or copelata work?

From Scientific American ● Oct. 5, 2023

In three appendices to his book, Turchin provides a non-technical explanation of his approach to understanding history and how it developed over time.

From Salon ● Jun. 25, 2023

I had finished the appendices of The Lord of the Rings, but I still had some econ reading left.

From "Darius the Great Is Not Okay" by Adib Khorram

The report, a mere nine pages including two appendixes, does not identify the mysterious unidentified phenomena—neither as mundane human technology nor anything extraterrestrial.

From Slate ● Jun. 29, 2021

The 35-page ARB document, with heavily redacted appendixes, was obtained under the Freedom of Information Act by the National Security Archive, a Washington-based, nonprofit research organization, which provided it to The Washington Post.

From Washington Post ● Feb. 10, 2021

If you want more practical help than that, Saunders provides some exercises in the appendixes.

From Los Angeles Times ● Jan. 7, 2021

Host Meagan Cantwell talks with Viviane Labrie of the Van Andel Institute in Grand Rapids, Michigan, about new research suggesting people without their appendixes have a reduced risk of Parkinson’s.

From Science Magazine ● Nov. 1, 2018

In hospitals in which the reimbursement rates for appendectomies ran higher, for instance, the surgeons removed more appendixes.

From "The Big Short" by Michael Lewis

Related Words

• addendum
• postscript