[ meyn-lahyn, -lahyn ]
/ ˈmeɪnˌlaɪn, -ˈlaɪn /
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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.



In effect, this quiz will prove whether or not you have the skills to know the difference between “affect” and “effect.”
Question 1 of 7
The rainy weather could not ________ my elated spirits on my graduation day.

Origin of mainline

1935–40, Americanism; v., adj. use of main line

Definition for mainline (2 of 3)

main line


a principal line or route of a railroad, as contrasted with a branch or secondary one.
a principal highway.
  1. a prominent and readily accessible vein of the body that may be used for a narcotic's injection.
  2. the act of mainlining.

Origin of main line

First recorded in 1835–45

Definition for mainline (3 of 3)

Main Line


a fashionable residential district west of Philadelphia.
any fashionable district where socially prominent people live.
Main-Line, adjectiveMain-Liner, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2021

British Dictionary definitions for mainline

main line


  1. the trunk route between two points, usually fed by branch lines
  2. (as modifier)a main-line station
US a main road

verb mainline

(intr) slang to inject a drug into a vein

adjective mainline

having an important position, esp having responsibility for the main areas of activity
mainliner, noun
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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