from The American Heritage® Dictionary of the English Language, 4th Edition
- n. An underground urban railroad, usually operated by electricity.
- n. A passage for such a railroad.
- n. An underground tunnel or passage, as for a water main or for pedestrians.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. An underground railway, especially for mass transit of people in urban areas.
- n. A rapid transit system, regardless of the elevation of its right of way.
- n. underground walkway, tunnel for pedestrians (called pedestrian underpass in US).
- v. To travel by underground railway.
from the GNU version of the Collaborative International Dictionary of English
- n. An underground way or gallery; especially, a passage under a street, in which water mains, gas mains, telegraph wires, etc., are conducted.
- n. An underground railroad, usually having trains powered by electricity provided by an electric line running through the underground tunnel. It is usually confined to the center portion of cities; -- called also tube, and in Britain, underground. In certain other countries (as in France or Russia) it is called the metro.
from The Century Dictionary and Cyclopedia
- n. An underground way; an accessible underground passage containing gas- and water-mains, telegraph-wires, etc.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. an underground tunnel or passage enabling pedestrians to cross a road or railway
- n. an electric railway operating below the surface of the ground (usually in a city)
sub- ("under") + way (Wiktionary)