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mainline

[meyn-lahyn, -lahyn]
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verb (used without object), main·lined, main·lin·ing. Slang.
  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), main·lined, main·lin·ing. Slang.
  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.
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adjective
  1. having a principal, established, or widely accepted position; major; mainstream: the membership of mainline churches.
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Origin of mainline

1935–40, Americanism; v., adj. use of main line
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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Word Origin and History for mainlining

mainline

v.

also main-line, 1934, from main line in American English slang sense "principal vein into which drugs can be injected" (1933).

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Online Etymology Dictionary, © 2010 Douglas Harper