1) Boat for duck shooting 2) Great Lakes boat 3) Great Lakes hunting boat 4) Heroin 5) Karl Malden TV series of 1980 6) Street names for heroin 
Skag is a short-lived American drama series that aired on NBC and starred Karl Malden. Skag originated as a three-hour television movie that aired on January 6, 1980 (as an installment of The Big Event). Over a week later, it then premiered as a weekly series, Thursdays at 10/9c, which ran from January 17, 1980 until its cancellation on February 2...
• (n.) An additional piece fastened to the keel of a boat to prevent lateral motion. See Skeg.
Skag noun (Nautical) An additional piece fastened to the keel of a boat to prevent lateral motion. See Skeg . 
Skag (scag) is slang for a cigarette or cigarette stub.