Webster's Shelfmate is a reference book published by Merriam-Webster, Inc. It is a companion to the popular Roget's Thesaurus, which is also published by Merriam-Webster. The two books are designed to be used together, with Roget's providing synonyms and antonyms for words, and Webster's Shelfmate providing definitions and examples of usage. Together, they provide a comprehensive resource for writers, students, and anyone looking to expand their vocabulary.