I. | ̷ ̷ ̷ ̷| ̷ ̷ adverb
Etymology: under (II) + ground, n.
1. : beneath the surface of the earth
water flowing underground
burrowing underground
2. : in or into hiding or secret operation
an ideology driven underground develops into a more virulent form — W.O.Douglas
the association soon became subversive and went underground — Harold Ingrams
II. ˈ ̷ ̷ ̷ ̷ˌ ̷ ̷ adjective
1. : being, growing, or situated below the surface of the ground
underground cave
underground cellar
underground stream
underground rhizomes
2. : dwelling in an underworld
mythical underground people
3. : used or adapted for use or wear underground : employed or performing duties underground
underground foreman
underground shovel
4. : done or occurring underground especially away from public knowledge : conducted or conveyed by secret or stealthy means
underground revolutionary activity
the underground life of civilized societies — Edward Sapir
III. noun
Etymology: underground (II)
1. : the space or place beneath the surface of the ground : a subterranean space or channel
2. : ground or soil lying beneath the surface or beneath something else
3. : an underground city railway system
the London Underground
4.
a. : a movement or group organized in strict secrecy among citizens in an occupied or totalitarian country for maintaining communications, popular solidarity, and concerted resistive action pending liberation
the underground in Occupied France
b. : a clandestine conspiratorial cell or organization set up for revolutionary or other disruptive purposes especially against a civil order — used with the
the Communist underground in wartime Germany
IV. adjective
1.
a. : existing outside the establishment or mainstream
an underground literary reputation
b. : existing outside the purview of tax collectors or statisticians
the underground economy
2.
a. : produced or published outside the establishment especially by the avant-garde
underground movies
underground newspapers
b. : of or relating to the avant-garde underground
an underground theater
V. noun
: a usually avant-garde group or movement that functions outside the establishment
VI. ¦ ̷ ̷ ̷ ̷ ¦ ̷ ̷ transitive verb
Etymology: underground (I)
: to place underground
undergrounding power lines