From The Collaborative International Dictionary of English v.0.48 [gcide]:
Subway \Sub"way`\, n.
1. An underground way or gallery; especially, a passage under
a street, in which water mains, gas mains, telegraph
wires, etc., are conducted.
[1913 Webster]
2. 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.
[PJC]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Underground \Un"der*ground`\, a.
1. Being below the surface of the ground; as, an underground
story or apartment.
[1913 Webster]
2. Done or occurring out of sight; secret. [Colloq.]
[1913 Webster]
Underground railroad or Underground railway. See under
Railroad.
[1913 Webster]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Underground \Un"der*ground`\, n.
1. The place or space beneath the surface of the ground;
subterranean space.
[1913 Webster]
A spirit raised from depth of underground. --Shak.
[1913 Webster]
2. a subway or subway system, especially in the United
Kingdom. [chiefly British]
[PJC]
3. a secret organization opposed to the prevailing
government; as, the French underground during the Nazi
occupation.
[PJC]
4. a group or movement holding unorthodox views in an
environment where conventional ideas dominate, as in
artistic circles.
[PJC]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Underground \Un"der*ground`\, adv.
Beneath the surface of the earth.
[1913 Webster]
From WordNet (r) 3.0 (2006) [wn]:
underground
adv 1: in or into hiding or secret operation; "the organization
was driven underground"
2: beneath the surface of the earth; "water flowing underground"
adj 1: under the level of the ground; "belowground storage
areas"; "underground caverns" [syn: belowground,
underground]
2: conducted with or marked by hidden aims or methods;
"clandestine intelligence operations"; "cloak-and-dagger
activities behind enemy lines"; "hole-and-corner intrigue";
"secret missions"; "a secret agent"; "secret sales of arms";
"surreptitious mobilization of troops"; "an undercover
investigation"; "underground resistance" [syn: clandestine,
cloak-and-dagger, {hole-and-corner(a)}, hugger-mugger,
hush-hush, secret, surreptitious, undercover,
underground]
n 1: a secret group organized to overthrow a government or
occupation force [syn: underground, resistance]
2: an electric railway operating below the surface of the ground
(usually in a city); "in Paris the subway system is called
the `metro' and in London it is called the `tube' or the
`underground'" [syn: metro, tube, underground, {subway
system}, subway]