Here’s a classic web tool if ever there was one.
Twists, Slugs, and Roscoes: a Glossary of Hardboiled Slang has been on the Internet since 1993. As the name suggests, it’s a glorious collection of terms straight out of the noir pulps and movies, and comes complete with its own bibliography. It’s perfect to spice up any gangster-era game.
So glom that list you ginks, before I make you chew a gat.