Definition from Wiktionary, the free dictionary
mainline (not comparable)
- Normal, principal or standard.
- (rail transport) Of or pertaining to the principal route or line of a railway.
- (rail transport) Of or pertaining to a surface railway as distinct from an underground, elevated or light rail one.
- (normal, principal or standard): mainstream
mainline (plural mainlines)
- (aviation) An airline's main operating unit, as opposed to codeshares or regional subsidiaries.
- (computing) The main repository for a software project, from which different versions (forks) may be split off.