Vocabulum; or The Rogue's Lexicon Compiled from the Most Authentic Sources

"Vocabulum; or The Rogue's Lexicon" by George W. Matsell is a compilation of the secret language used by criminals in the mid-1800s. Its origin lies in the author’s experience as a police chief, who noticed the need to understand the special slang of the criminal world to do his job well. The author explains how criminals have their own language that changes and eventually sneaks into normal, everyday talk. The author shares the difficulty he had in writing down this slang, because it was mostly spoken. He makes it clear that knowing this language is important not only for police but for everyone, because this special language shows up in different ways in daily discussion.