underground
Americanadverb
adjective
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existing, situated, operating, or taking place beneath the surface of the ground. ground.
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used, or for use, underground.
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hidden or secret; not open.
underground political activities.
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published or produced by political or social radicals or nonconformists.
an underground newspaper.
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avant-garde; experimental.
an underground movie.
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critical of or attacking the established society or system.
underground opinion.
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of or for nonconformists; unusual.
an underground vegetarian restaurant.
noun
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the place or region beneath the surface of the ground. ground.
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an underground space or passage.
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a secret organization fighting the established government or occupation forces.
He fought in the French underground during the Nazi occupation of France.
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(often initial capital letter) a movement or group existing outside the establishment and usually reflecting unorthodox, avant-garde, or radical views.
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Chiefly British. a subway system.
verb (used with object)
adjective
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occurring, situated, or used below ground level
an underground tunnel
an underground explosion
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secret; hidden
underground activities
adverb
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going below ground level
the tunnel led underground
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into hiding or secrecy
the group was driven underground
noun
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a space or region below ground level
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a movement dedicated to overthrowing a government or occupation forces, as in the European countries occupied by the German army in World War II
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( as modifier )
an underground group
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US and Canadian equivalent: subway. an electric passenger railway operated in underground tunnels
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(usually preceded by the)
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any avant-garde, experimental, or subversive movement in popular art, films, music, etc
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( as modifier )
the underground press
underground music
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Etymology
Origin of underground
Vocabulary lists containing underground
Florida's B.E.S.T. Common Prefixes: under-
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Essential Question Vocabulary (Unit 5)
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Then he reluctantly answers a phone call from his ex-girlfriend as he’s making his way up from underground and she tells him she’s pregnant.
From Los Angeles Times • Apr. 10, 2026
Inside an underground shelter at a hospital in the Israeli city of Haifa, a television screen flickers with images of Iranian missiles as doctors and midwives deliver Sarah Bird's third child.
From Barron's • Apr. 10, 2026
Mexican army divers have rescued a miner from a flooded underground tunnel two weeks after he was first trapped.
From BBC • Apr. 9, 2026
Geothermal energy systems require electronics that can function deep underground, where surrounding rock can glow red-hot.
From Science Daily • Apr. 7, 2026
So we developed a system for coding our underground messages in terms of watches.
From "The Hiding Place" by Corrie ten Boom
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Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.