A commuter rail system that combines aspects of an interurban railway with those of a subway, using a menagerie of pathways such as viaduct, tunnel, beam, cut and cover, trench, at grade, and others.
An underground passage, subway, tunnel.
A voyage, especially underwater.
A road, track, path, or street for going under another way or obstacle; an underpass.
In motion, in progress; being done or carried out; on a journey.