Mainline

[Magaret]

To [inject] a drug, usually [heroin], into a [vein]. Also used to refer to the drug itself.

[Dave Paprocki]

To watch a large amount of a geeky television show, episode after episode, for a long period of time. A season of [Buffy] in two days, for example.
Similar to [marathoning] movies or [chain smoking], but more geeky.

[Vania]

A [persons] main [significant other], even though they may be dating several people [at once].

[Michiko]

A chief railway line.

[Julian]

involving beliefs, methods, etc. that are most common: