the principal road, course, etc.
having a principal, prominent, or moderate position or status
Slang to inject (a narcotic drug) directly into a large vein
verbmain·lined, main·lin·ing, main·lines Informal
To inject (an illegal or addictive drug, such as heroin) directly into a major vein.
To inject a drug intravenously.
Being in a principal or well-established position: the mainline churches.
(third-person singular simple present mainlines, present participle mainlining, simple past and past participle mainlined)