verb (used without object), main·lined, main·lin·ing. Slang.
- to inject a narcotic, especially heroin, directly into a vein.
- to use or enjoy something without restriction: to mainline on TV movies.
verb (used with object), main·lined, main·lin·ing. Slang.
- to inject (a narcotic, especially heroin) directly into a vein.
- to use, enjoy, or imbibe (something) without restriction: mainlining coffee all day long.
- having a principal, established, or widely accepted position; major; mainstream: the membership of mainline churches.
v.also main-line, 1934, from main line in American English slang sense “principal vein into which drugs can be injected” (1933).