What does appendix mean?
An appendix is a supplementary section appended to the end of a book, report, or academic paper, used to present supporting material — raw data, detailed tables, transcripts, or methodological notes — that would clutter the main text. The plural is usually 'appendices', though 'appendixes' is also accepted. The word has a second, entirely distinct life in anatomy: the appendix is the small, finger-shaped pouch that projects from the cecum at the junction of the small and large intestines. Long labeled a vestigial organ with no function, it has more recently been implicated in immune and gut-flora-related roles, though its removal (an appendectomy) is routine and generally harmless. Inflammation of this organ, appendicitis, is a medical emergency, making 'a burst appendix' one of the most familiar phrases in everyday health vocabulary. Whether in publishing or medicine, the word conveys something added on — fittingly, since its Latin root means 'to hang upon'.
A section of supplementary material, such as tables, documents, or data, placed at the end of a book or report.
"The statistical tables are provided in the appendix for readers who want the full detail."
Plural: appendices (classical) or appendixes (also standard).
The vermiform appendix: a narrow, tube-shaped pouch projecting from the cecum at the beginning of the large intestine.
"Surgeons removed her inflamed appendix before it could rupture."
'Appendices' is the traditional Latinate plural and remains preferred in formal, academic, and publishing contexts; 'appendixes' is equally correct and common in general and medical American usage.
"The report runs to four appendices covering methodology, raw data, and correspondence."
The human appendix was dismissed for over a century as a useless evolutionary leftover — but modern research suggests it may act as a safe house for beneficial gut bacteria.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of appendix
Appendix comes from Latin appendix, meaning 'something attached or hung on', derived from the verb appendere, 'to hang upon', formed from ad- ('to') plus pendere ('to hang'). It entered English in the early 16th century, initially in general senses before settling into its modern bibliographic and anatomical uses. The same Latin root gives English a family of related words including depend, suspend, expend, and pendant, all built on the idea of hanging or weighing.
Related word forms
How appendix is actually used
In anatomy, 'the appendix' almost always refers to the vermiform appendix of the intestine, and the word is typically used without an article in casual speech ('she had her appendix out'). The classical plural 'appendices' is standard in scholarly and publishing contexts, though 'appendixes' is fully acceptable, especially in American English and medical writing.
Easily confused with appendix
Appendicitis is the inflammation of the appendix, whereas the appendix itself is the anatomical structure (or, in books, the supplementary section).
An addendum is material added after a document's publication to correct or update it, while an appendix is planned supplementary material included at the end of the original work.