mainline

American  

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

verb (used without object)

Slang.

mainlined, mainlining

1. to inject a narcotic, especially heroin, directly into a vein.

2. to use or enjoy something without restriction.

   to mainline on TV movies.

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verb (used with object)

Slang.

mainlined, mainlining

1. to inject (a narcotic, especially heroin) directly into a vein.

2. to use, enjoy, or imbibe (something) without restriction.

   mainlining coffee all day long.

adjective

1. having a principal, established, or widely accepted position; major; mainstream.

   the membership of mainline churches.

Etymology

Origin of mainline

1935–40, v., adj. use of main line

Example Sentences

It is the main station for all services on the west coast mainline to England and also operates services throughout central Scotland.

From BBC • Mar. 10, 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

The tax burden would be disproportionately felt by progressive mainline Protestant churches, Black evangelical churches and immigrant-majority Catholic and Protestant congregations, not to mention immigrant-majority mosques and temples.

From Salon • Nov. 16, 2025

Alaska faced a similar outage just three months ago when a critical piece of hardware at a data center failed, bringing down its systems and forcing it to cancel about 10% of its mainline schedule.

From The Wall Street Journal • Oct. 24, 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

Related Words

• dominant
• key
• leading
• main
• major
• outstanding
• paramount
• predominant
• preeminent
• primary
• prime
• prominent