mainlined; mainlining; mainlines
slang
: to take by or as if by injecting into a principal vein
slang
: to mainline a narcotic drug
: being part of an established group
also
: being in the mainstream
1
: a principal highway or railroad line
2
slang
: a principal vein of the circulatory system
Examples of mainline in a Sentence
Verb
His addiction grew worse when he began mainlining.
Recent Examples on the Web
Michael Deeds, Idaho Statesman, 10 Mar. 2026
Anderson’s composer, Jonny Greenwood (from Radiohead), alternates tones of wailing electronic despair and a pounding rhythm that mainlines energy.
—David Denby, New Yorker, 9 Mar. 2026
ArsTechnica, 19 May 2026
The Forest Service approved chainsaw work on 61 trails, most of which are considered mainline or secondary trails — the primary routes in the wilderness and the initial offshoots that branch from them.
—Nicole Blanchard, Idaho Statesman, 14 May 2026
Doug Ross, Chicago Tribune, 5 Apr. 2026
As far as a solution to our big number two problem, there are two main lines of thinking.
—Andrew Paul, Popular Science, 25 Mar. 2026
See All Example Sentences for mainline
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Verb
Start mainlining Centrum Silver, Boise.
—Michael Deeds, Idaho Statesman, 10 Mar. 2026
Anderson’s composer, Jonny Greenwood (from Radiohead), alternates tones of wailing electronic despair and a pounding rhythm that mainlines energy.
—David Denby, New Yorker, 9 Mar. 2026
Adjective
That was the promise on the box of Sid Meier’s Civilization, the first in a long-running strategy game franchise that has evolved over 35 years and seven mainline entries.
—ArsTechnica, 19 May 2026
The Forest Service approved chainsaw work on 61 trails, most of which are considered mainline or secondary trails — the primary routes in the wilderness and the initial offshoots that branch from them.
—Nicole Blanchard, Idaho Statesman, 14 May 2026
Noun
Construction has finally started for the trail to go under the Norfolk Southern main line.
—Doug Ross, Chicago Tribune, 5 Apr. 2026
As far as a solution to our big number two problem, there are two main lines of thinking.
—Andrew Paul, Popular Science, 25 Mar. 2026
See All Example Sentences for mainline
Cite this Entry
“Mainline.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/mainline. Accessed 20 May. 2026.
Copy CitationMedical Definition
mainline
1 of 2 verb
main·line
ˈmān-ˈlīn 
mainlined; mainlining
slang
: to take by or as if by injecting into a principal vein
slang
: to mainline a narcotic drug (as heroin)
main line
2 of 2 noun
slang
: a principal vein of the circulatory system
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