"Roget's Thesaurus" by Peter Mark Roget is a reference work first published in 1852. Roget, a British physician and lexicographer, created this revolutionary system of verbal classification to help writers struggling with composition. Rather than arranging words alphabetically, his thesaurus organizes them into six primary classes with over a thousand meaning clusters, grouping words by semantic relationships and conceptual connections. Originally containing 15,000 words, the work has expanded through successive editions while maintaining Roget's foundational organizational system, becoming one of the most widely used English-language reference tools.