1. a principal line or route of a railroad, as contrasted with a branch or secondary one.
2. a principal highway.
a. a prominent and readily accessible vein of the body that may be used for a narcotic's injection.
b. the act of mainlining.
1. a fashionable residential district west of Philadelphia.
2. any fashionable district where socially prominent people live.
Pronunciation: (mān'līn", -līn'), [key]
—v., -lined, -lin•ing,
1. to inject a narcotic, esp. heroin, directly into a vein.
2. to use or enjoy something without restriction: to mainline on TV movies.
1. to inject (a narcotic, esp. heroin) directly into a vein.
2. 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.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.