Top Definition
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 10, 2008
1 more definition
the act of taking internet lingo and applying it to real life conversation

matt: I walked by a group of kids taking a test and said, "fucking scrubs."
joel: dude, you were totally mainlining.
by Taxt April 16, 2009

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