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Meaning of “underground” in the English Dictionary

"underground" in British English

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undergroundadjective, adverb

uk   /ˌʌn.dəˈɡraʊnd/  us   /ˌʌn.dɚˈɡraʊnd/
  • underground adjective, adverb (BELOW EARTH)

B2 below the surface of the earth; below ground: an underground cave/passage/cable Moles live underground.

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  • underground adjective, adverb (SECRET)

An underground activity is secret and usually illegal: an underground newspaper/movement The Communist Party was forced (to go) underground, and its leaders went into hiding.
the underground railroad
a secret system, used in the 19th century, by which slaves (= people who had been sold and forced to work) in the southern US were helped to escape to places where there was no slavery

undergroundnoun

uk   /ˈʌn.də.ɡraʊnd/  us   /ˈʌn.dɚ.ɡraʊnd/
  • underground noun (TRANSPORT)

the underground A2 [S] (also the tube) UK
a railway system in which electric trains travel through tunnels below ground: the London Underground They went on the underground.
(Definition of underground from the Cambridge Advanced Learner’s Dictionary & Thesaurus © Cambridge University Press)

"underground" in American English

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undergroundadjective, adverb [not gradable]

 us   /ˌʌn·dərˈɡrɑʊnd/
below the surface of the earth; below ground: an underground garage
Something that is done underground is secret or hidden, usually because it is not traditional or is shocking or illegal: an underground newspaper Officials believe the sighting of the suspect may have forced him to go underground (= to become secret).

undergroundnoun [U]

 us   /ˈʌn·dərˌɡrɑʊnd/
The underground is an organization that secretly works against those in power: He was a member of the French underground in World War II.
(Definition of underground from the Cambridge Academic Content Dictionary © Cambridge University Press)
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“underground” in American English

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