adj
- Of or pertaining to the principal route or line of a railway.
- Normal, principal or standard.
- Of or pertaining to a surface railway as distinct from an underground, elevated or light rail one.
- Of a sequence of opening moves: being part of a main line ("a standard sequence of opening moves considered to be best play").
noun
- The principal route or line of a railway.
- In longline fishing the central line to which the branch lines with baits are attached.
- An airline's main operating unit, as opposed to codeshares or regional subsidiaries.
- A principal vein into which a drug can be injected.
- The main repository for a software project, from which different versions (forks) may be split off.
- The pipeline carrying wastewater to the public drains or a septic tank.
verb
to find a better fitting word. Finally, thanks to ChatGPT, the overall results have been greatly improved.