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Fun Holiday – Thesaurus Day

January 18 is Thesaurus Day. Impress your family and friends with big, complicated, and fancy sounding words to celebrate this lexicographic holiday.

18 Jan
Thesaurus Day
Sunday, January 18, 2026
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The word strategy written in a thesaurus.
The word thesaurus comes from the Greek word for treasury or storehouse.
©bigstockphoto.com/Simon Valentine

The unofficial holiday commemorates the birth anniversary of British lexicographer and physician, Peter Mark Roget, the author of the Roget’s Thesaurus.

Storehouse of Words

A thesaurus is a book that compiles words grouped by similarity of meaning. The term thesaurus comes from the Greek word, thesauros, meaning treasure or storehouse.

Roget's Thesaurus is one of the most widely used reference books in the English language around the world. It was first published in 1852 with 15,000 words. Since then, the book has never gone out of publication.

Therapeutic Origins

It is believed that Roget worked on making word lists that later became the Roget's Thesaurus as a way to combat with depression and mental illness. Roget is also known for inventing the log slide rule in 1814. The slide rule helps calculate the roots of number very easily.

How to Celebrate?

  • Bring out your thesaurus and carry it with you the whole day, using it every time you want to speak with someone.
  • Play a game of Synonym.

Did You Know…

…that synonym is an antonym of antonym?

Thesaurus Day Observances

Year Weekday Date Name
2025 Sat Jan 18 Thesaurus Day
2026 Sun Jan 18 Thesaurus Day
2027 Mon Jan 18 Thesaurus Day
2028 Tue Jan 18 Thesaurus Day
2029 Thu Jan 18 Thesaurus Day
2030 Fri Jan 18 Thesaurus Day
2031 Sat Jan 18 Thesaurus Day
2032 Sun Jan 18 Thesaurus Day
2033 Tue Jan 18 Thesaurus Day
2034 Wed Jan 18 Thesaurus Day