°Below the ground; below the surface of the Earth.
"There is an underground tunnel that takes you across the river."
°Hidden, furtive, secretive.
"These criminals operate through an underground network."
verb
°Below the ground.
°Secretly.
noun
°(with "the") A movement or organisation of people who resist political convention.
synonyms:
subterranean, clandestine, hidden, hush-hush
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, secret, avant-garde, unconventional, below, ground, clandestinely, in secret, on the quiet, metro, métro, subway, tube, resistance, avant-garde, counter-culture