George W. Matsell's "Vocabulum; or The Rogue's Lexicon" serves as a fascinating exploration of the secret language used by criminals in 19th-century America. Written in the vivid and engaging style characteristic of early lexicography, this book meticulously catalogues the unique terms and slang employed by rogues, con artists, and outlaws. The lexicon not only functions as a linguistic resource but also provides readers with insights into the societal attitudes and cultures surrounding crime during a transformative period in American history. Each entry is illustrated with context and anecdotal evidence, effectively situating the language within its literary and social milieu. George W. Matsell, a New York City police officer, possessed firsthand experience with the criminal underworld he aimed to document. His intimate knowledge of the vernacular spoken among criminals stems from his career, where he encountered these individuals in various law enforcement roles. Matsell's dedication to demystifying criminal slang was partly a reflection of his commitment to understanding and, ultimately, combating crime in a burgeoning urban landscape. This book is a must-read for enthusiasts of linguistics, social history, and criminal justice, providing a rich tapestry of language that highlights the intersection of culture and crime. "Vocabulum" not only enriches our understanding of historical slang but also serves as a testament to the complexities of human communication in the face of societal challenges.