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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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
Within hours of the initial strikes on Iran, major hospitals across Israel shifted to maximum emergency readiness, moving patients and critical departments underground.
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
All members of the Satyrex genus are fossorial, meaning they spend their lives underground.
From Science Daily • Apr. 6, 2026
The map showed clearly that they must begin their climb at the place where the water gushed from its underground tunnel to form the stream.
From "Rowan of Rin" by Emily Rodda
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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.