main line in British English
noun
1. railways
a.
the trunk route between two points, usually fed by branch lines
b.
(as modifier)
a main-line station
2. US
a main road
verb mainline
3. (intransitive) slang
to inject a drug into a vein
adjective mainline
4.
having an important position, esp having responsibility for the main areas of activity
Derived forms
mainliner (ˈmainˌliner) noun