underpass

from WordNet (r) 3.0 (2006)

underpass
    n 1: an underground tunnel or passage enabling pedestrians to
         cross a road or railway [syn: {underpass}, {subway}]

from Moby Thesaurus II by Grady Ward, 1.0

37 Moby Thesaurus words for "underpass":
      access, aisle, alley, ambulatory, aperture, arcade, artery, avenue,
      channel, cloister, colonnade, communication, conduit, connection,
      corridor, covered way, defile, exit, ferry, ford, gallery, inlet,
      interchange, intersection, junction, lane, opening, outlet,
      overpass, pass, passage, passageway, portico, railroad tunnel,
      traject, trajet, tunnel