The term “Roget's Thesaurus” is used to describe the book that was written by Peter Mark Roget in 1852. It is believed that he wrote this book as a way of combating his depression and mental illness. Roget's Thesaurus is a widely used English-language thesaurus, created in 1805 by Peter Mark Roget (1779–1869), a British physician, natural theologian, and lexicographer. It was released to the public on 29 April 1852. The first edition of this book had 15,000 words and each successive edition has been larger, with the most recent edition containing 443,000 words.    

National Thesaurus Day is observed annually on January 18th!

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