verb (used without object), main·lined, main·lin·ing. Slang.
verb (used with object), main·lined, main·lin·ing. Slang.
Origin of mainline
Examples from the Web for mainline
And mainline Protestant denominations find themselves shrinking.
Mainline Protestant denominations are in marked decline and Evangelical Christianity is in slow retrograde.
This collaboration is different from our mainline collection, but the PETER PILOTTO woman is the same.Peter Pilotto Makes Target Go Pop in Latest Collaboration|The Fashion Beast Team|February 7, 2014|DAILY BEAST
The decline of mainline Protestantism has also undermined this sort of prudent, empirically-minded Republicanism.
Mainline Republicans like Mitch McConnell backed the losing candidate in the Republican primary.Midterm Madness: McCain, Reid, & 10 Hot Races to Watch|Samuel P. Jacobs|August 22, 2010|DAILY BEAST
Sidetrack your emotions if you can and stick to the mainline!Cleek of Scotland Yard|Thomas W. Hanshew
Word Origin and History for mainline
also main-line, 1934, from main line in American English slang sense "principal vein into which drugs can be injected" (1933).