Definitions from Wiktionary ( )

▸ adjective:  Normal, principal or standard.
▸ adjective:  (rail transport) Of or pertaining to the principal route or line of a railway.
▸ adjective:  (rail transport) Of or pertaining to a surface railway as distinct from an underground, elevated or light rail one.
▸ adjective:  (chess) Of a sequence of opening moves: being part of a main line ("a standard sequence of opening moves considered to be best play").
▸ verb:  (slang) To inject (a drug) directly into a vein.
▸ verb:  (by extension, informal, transitive) To consume voraciously.
▸ verb:  (computing, transitive) To integrate (code, etc.) into the main repository for a software project, rather than separate forks.
▸ verb:  (transitive) To include (a prisoner) in the general population of a prison.
▸ noun:  (aviation) An airline's main operating unit, as opposed to codeshares or regional subsidiaries.
▸ noun:  (rail transport) The principal route or line of a railway.
▸ noun:  (fishing) In longline fishing the central line to which the branch lines with baits are attached.
▸ noun:  (plumbing) The pipeline carrying wastewater to the public drains or a septic tank.
▸ noun:  (slang) A principal vein into which a drug can be injected.
▸ noun:  (computing) The main repository for a software project, from which different versions (forks) may be split off.
▸ noun:  The general population of a prison.
▸ noun:  (chess) Alternative form of main line [(chess) A standard sequence of opening moves considered to be best play.]

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