National Thesaurus Day | January 18
(Last Updated On: January 11, 2023)


National Thesaurus Day, on January 18th, honors Peter Mark Roget, the author of Roget’s Thesaurus, who was born on this day in 1779.  


In 1840, Roget retired from a successful career in medicine and spent the rest of his life working on Roget’s Thesaurus of English Words and Phrases. The work was the result of decades of collecting lists of words and categorizing them, much like a scientist would collect specimens. In Roget’s case, he collected words. He first published his thesaurus in 1852. And it was more than a book of synonyms – it was a complete categorization and organization of each word by meaning. 

Since then, poets and writers have used the thesaurus to help make their writing come to life. However, the thesaurus also has its detractors. Some say the thesaurus weakens language and destroys it. 

Whether you are looking for a more accurate word or trying to improve your writing, the thesaurus can be your best friend. Expanding your vocabulary increases both written and spoken communication skills, creative writing abilities, and can be helpful in advancing your career.


Use a thesaurus to find the right word for your writing. Play a word game to expand your vocabulary. Explore the bookstore and discover a new (or old) thesaurus to page through. Challenge friends to describe each other with as many words as possible without using the thesaurus. Then see how their descriptions improve when they do. Use #NationalThesaurusDay to post on social media.

Educators and Families, visit the National Day Calendar Classroom to discover more ways to celebrate with your students!


While the day commemorates the birth of Peter Mark Roget, our research did not identify the founder of the observance. However, we did find new words to add to our lexicon. 

Thesaurus FAQ

Q. Does a thesaurus only contain synonyms?
A. No. A thesaurus also lists antonyms, idioms, and related phrases.

Q. Does a thesaurus include definitions?
A. Usually a thesaurus does not include definitions. However, some are accompanied by a dictionary section that supplies definitions.

Q. What is the plural of thesaurus?
A. The plural form of thesaurus is either thesauri or thesauruses.

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