An airline's main operating unit, as opposed to codeshares or regional subsidiaries.
The main repository for a software project, from which different versions (forks) may be split off.
To inject (a drug) directly into a vein.
To integrate (code, etc.) into the main repository for a software project, rather than separate forks.
Normal, principal or standard.
Of or pertaining to the principal route or line of a railway.
Of or pertaining to a surface railway as distinct from an underground, elevated or light rail one.