the·​sau·​rus thi-ˈsȯr-əs How to pronounce thesaurus (audio)
plural thesauri thi-ˈsȯr-ˌī How to pronounce thesaurus (audio)
or thesauruses thi-ˈsȯr-ə-səz How to pronounce thesaurus (audio)
: a book of words or of information about a particular field or set of concepts
especially : a book of words and their synonyms
: a list of subject headings or descriptors usually with a cross-reference system for use in the organization of a collection of documents for reference and retrieval
thesaural adjective

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In the early 19th century, archaeologists borrowed the Latin word thesaurus to denote an ancient treasury, such as that in a temple. Soon after, the word was metaphorically applied to a book containing a treasury of words or information about a particular field. In 1852, the English scholar Peter Mark Roget published his Thesaurus of English Words and Phrases, in which he listed a treasury of semantically related words organized into numerous categories. This work led to the common acceptance of the term thesaurus to refer to "a book of words and their synonyms." The word developed another meaning in the 1950s, when thesaurus began being used in the field of word processing to refer to a list of related terms used for indexing and retrieval.

Example Sentences

Recent Examples on the Web Accordingly, to try to describe the near $110 billion the US has pledged to Ukraine in the last year sends one scrambling for a thesaurus. Thomas Sadoski, CNN, 2 Mar. 2023 The novels McCarthy published in 2022, at the age of 89, permanently resolve the question of whether McCarthy is a great novelist, or Louis L’Amour with a thesaurus. Graeme Wood, The Atlantic, 5 Dec. 2022 So why does this paper seem to have been co-written by a thesaurus? Neuroskeptic, Discover Magazine, 27 Jan. 2021 Joniak might need a thesaurus as Justin Fields’ career takes flight for the Bears. Brad Biggs, Chicago Tribune, 7 Nov. 2022 After Jokic scorched the Spurs again in October for 32 points and 16 rebounds in a 102-96 Nuggets win in Denver, coach Gregg Popovich exhausted his thesaurus describing the 26-year-old’s greatness. Jeff Mcdonald, San Antonio Express-News, 9 Dec. 2021 Over-the-top rhetoric that sounds as if someone locked Kiley in a room with a thesaurus, but doesn’t really conform to what even Newsom’s critics think of his performance. Michael Hiltzik, Los Angeles Times, 15 Sep. 2021 Books, including a thesaurus so tattered from use that back when there were regular tours of the newsroom, the tour guide would show it to visitors. Karina Bland, The Arizona Republic, 23 June 2021 Synonymy—the concept of distinct words signifying the same thing—was understood as far back as Ancient Greece, but the Archbishop of Seville authored the earliest work modern readers might recognize as a thesaurus. Claudia Kalb, Smithsonian Magazine, 21 Apr. 2021 See More

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'thesaurus.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Word History


New Latin, from Latin, treasure, collection, from Greek thēsauros

First Known Use

circa 1823, in the meaning defined at sense 2

Time Traveler
The first known use of thesaurus was circa 1823


Dictionary Entries Near thesaurus

Cite this Entry

“Thesaurus.” Dictionary, Merriam-Webster, Accessed 26 Mar. 2023.

Kids Definition


the·​sau·​rus thi-ˈsȯr-əs How to pronounce thesaurus (audio)
plural thesauri -ˈsȯ(ə)r-ˌī How to pronounce thesaurus (audio)
or thesauruses -ˈsȯr-ə-səz How to pronounce thesaurus (audio)
: a book of words and their synonyms

from scientific Latin thesaurus "treasury, storehouse, book of words," from Latin thesaurus "treasure, collection," from Greek thēsauros (same meaning) — related to treasure

Last Updated: - Updated example sentences
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