encyclopedia

American  

[en-sahy-kluh-pee-dee-uh] / ɛnˌsaɪ kləˈpi di ə /

Sometimes encyclopaedia

noun

1. a book, set of books, optical disc, mobile device, or online informational resource containing articles on various topics, usually in alphabetical arrangement, covering all branches of knowledge or, less commonly, all aspects of one subject.

2. Encyclopedia, the French work edited by Diderot and D'Alembert, published in the 18th century, distinguished by its representation of the views of the Enlightenment.

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encyclopedia British  

/ ɛnˌsaɪkləʊˈpiːdɪə /

noun

1. a book, often in many volumes, containing articles on various topics, often arranged in alphabetical order, dealing either with the whole range of human knowledge or with one particular subject

   a medical encyclopedia

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Etymology

Origin of encyclopedia

First recorded in 1525–35; from New Latin encyclopaedia, from Greek enkyklopaidía, a misreading of enkýklios paideía “circular (i.e., well-rounded) education”; see encyclical, pedo- ¹

Explanation

An encyclopedia is a reference work designed to cover all branches and topics of knowledge. We might describe someone who seems to know everything as a "walking encyclopedia." Encyclopedia comes the Greek words for "comprehensive" (cyclo) and "education" (pedia). The first encyclopedias were books (usually in many volumes), but now we have online and electronic encyclopedias. This reference is usually organized alphabetically and covers as many topics as possible. If you're doing research, the encyclopedia is a good place to start.

Example Sentences

As a child, he came across a page in an encyclopedia featuring Neil Armstrong and the picture of an astronaut on the Moon from the 1969 Apollo mission.

From BBC • Apr. 2, 2026

“I found the encyclopedia at the Underground,” he explains, of the DuBois work that became central to “Blknws.”

From Los Angeles Times • Mar. 4, 2026

He left behind a seminal 37-volume encyclopedia, the “Natural History,” and the surviving letters of his nephew paint a colorful portrait of a workaholic who rarely slept.

From The Wall Street Journal • Jan. 2, 2026

He maybe saw the idea of an A.I.-generated encyclopedia and wanted to be first to market.

From Slate • Nov. 17, 2025

He was an encyclopedia when it came to Xhosa genealogy and told me facts about my father that I had never known.

From "Long Walk to Freedom" by Nelson Mandela