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English definition of “underground”

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underground

adjective, adverb
 
 
/ˈʌndəɡraʊnd/
UNDER SURFACE B2 under the surface of the ground: underground caves an animal that lives undergroundGeology - general words
POLITICAL ACTIVITY Underground political activities are secret and illegal: an underground political organizationSecrecy and privacyTaking action against people in power
(Definition of underground adjective, adverb from the Cambridge Learners Dictionary © Cambridge University Press)
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