To inject a drug, usually heroin, into a vein. Also used to refer to the drug itself.
"That chick was mainlining heroin daily till she OD'd."

From Queensryche - Operation Mindcrime:

"Had a habit doing mainline
Watch the dragon burn
No regrets, you've got no goals
Nothing more to learn"
by eidolon July 18, 2004
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(n) The front-running leader(s) of an industry; not the imitation spin-offs. Reserved for the select few whom others try to imitate albeit never successfully. If you are not mainline you are hopeless and should probably just quit what you do, now.

(adj) Describing an action that would only be done by someone/something that is mainline.
Guy 1: Why does that guy drive such a shitty old car if he's a lawyer?

Guy 2: He must not be mainline. If he were, he would drive a BMW 5 Series.

Guy 1: Lebron James is overrated.

Guy 2: Seriously?! He is the most mainline basketball player of this generation.
by Reacharoundartist May 22, 2010
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Weaponized wireless telepathic communications and informations system used by covert US military-intelligence in the Targeted Individual program.
The military had their own voice-to-skull...they called it the mainline... it was voice-to-skull.
by Medicine Owl February 8, 2023
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the intravenous injection of a drug. which means using a needle to get a drug into your vein, to absorb it through your bloodstream. a lot of drugs can be taken this way, the most commonly associated drug being heroin.
Layne accidentally overdosed by mainlining heroin.
by two blue lights November 11, 2008
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One who does drugs such as heroin by means of shooting up in a vein. Intraveinously
by Kyleigh January 27, 2006
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One who injects drugs into their bloodstream with a needle.
Ohmygod, he's not only a mainliner, he reuses his works! Do not exchange any bodily fluids with him no matter what.
by mjrn February 26, 2006
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to render righteousness with perfect fidelity, especially using emerging information and communication technologies. A MKULTIMATE asset commandeered from MKULTRA.
During MKULTRA, every mainline was murder; now, we are fortunate to be able to MainLine America; now, every MainLine is a Miracle.
by Medicine Owl February 8, 2023
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