Definition of underground railway:
(n) :
(rail transport) Synonym of subway: a railway under the ground.
(n) :
Alternative form of Underground Railroad. [(historical) The pre-American Civil War anti-slavery resistance movement dedicated to helping escaped slaves to reach safe territory.]
(n) :
(usually capitalized) Alternative form of Underground Railroad. [(historical) The pre-American Civil War anti-slavery resistance movement dedicated to helping escaped slaves to reach safe territory.]