noun

• (Canada, US, Scotland, South Africa) An underground railway, especially for mass transit of people in urban areas.
  "He is going to Westminster by subway."
• (Canada, US, Scotland, South Africa) A train that runs on such an underground railway.
  "Just before you leave, the subway comes. You get on. It stops at the next station."
• (Canada, US) A rapid transit system, regardless of the elevation of its right of way; a metro system.
• (British) An underground walkway, tunnel for pedestrians (called pedestrian underpass in US).
  "At Nairobi the mail waits an hour-and-a-half. The station has three long platforms, mostly covered in awnings, the island connected with the main platform (which is used by the mails in both directions) by a subway."

verb

• (intransitive, US, informal) To travel by underground railway.
  "I suppose I could have subwayed around town in search of froufrou French pastry shops."