mainline
Americanverb (used without object)
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to inject a narcotic, especially heroin, directly into a vein.
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to use or enjoy something without restriction.
to mainline on TV movies.
verb (used with object)
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to inject (a narcotic, especially heroin) directly into a vein.
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to use, enjoy, or imbibe (something) without restriction.
mainlining coffee all day long.
adjective
Etymology
Origin of mainline
1935–40, v., adj. use of main line
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
It could have come to life as a lesser kind of Ferrari, a diminished derivative of one of the company’s mainline GT cars, with a turbocharged V8 under the hood.
From The Wall Street Journal • Apr. 18, 2026
The train operator LNER, which runs the east coast mainline, has extended its advice to passengers not to travel between Edinburgh and Aberdeen as they "cannot guarantee" trains will operate until Friday at the earliest.
From BBC • Jan. 6, 2026
In the financial year from April 2024 in the report to March 2025, passengers took 1.7 billion journeys on the mainline railway.
From BBC • Oct. 23, 2025
With that guidance, officials canceled plans to transfer most of the inmates to mainline prisons.
From The Wall Street Journal • Oct. 11, 2025
But over the last forty years, evangelicals have pulled steadily closer in income and education to mainline Protestants in the historically affluent establishment denominations.
From "Class Matters" by The New York Times
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
