Learn how to say Mainline correctly in English with this tutorial pronunciation video.
Oxford dictionary definition of the word main line:
1a chief railway line:
a main-line station
North American a chief road or street.
2 informal a principal vein as a site for a drug injection.
(mainline) [with object] informal inject (a drug) intravenously:
Mariella mainlines cocaine five times a day
he started mainlining on heroin