Definify.com
Webster 1913 Edition
Underground
Un′der-groundˊ
,Noun.
1.
The place or space beneath the surface of the ground; subterranean space.
A spirit raised from depth of
underground
. Shakespeare
Un′der-groundˊ
,Adj.
1.
Being below the surface of the ground;
as, an
. underground
story or apartment2.
Done or occurring out of sight; secret.
[Colloq.]
Underground railroad
or Underground railway
See under
Railroad
.Un′der-groundˊ
,adv.
Beneath the surface of the earth.
Webster 1828 Edition
Underground
UNDERGROUND'
,Noun.