the word "slug" has a variety of definitions:
1. a bullet
2. a shot (of liquor)
3. to punch or knock unconscious
these definitions can often be found in hard-boiled detective fiction popularized by writers such as Raymond Chandler and Dashiell Hammett in the 1930s and 1940s.
1. I fired a couple of slugs into the air to let them know I meant business.
2. I downed a couple of slugs at the speakeasy.
3. You shut your yap before I slug you.