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/ˌʌn.dəˈɡɹaʊnd/ · adjective
(not comparable) Below the ground; below the surface of the Earth..
There is an underground tunnel that takes you across the river.
One of the hidden glories of Victorian engineering is proper drains. Isolating a city’s effluent and shipping it away in underground sewers has probably saved more lives than any medical procedure except vaccination.
These criminals operate through an underground network.
underground music
‘[…]he wrote to me last week telling me about an incredible bitch of a row blazing there on account of someone having been and gone and produced an unofficial magazine called Raddled, full of obscene libellous Oz-like filth. And what I though, what Sammy and I thought, was—why not?’ ‘Why not what?’ said Tom. ‘Why not do the same thing here?’ ‘You mean an underground magazine?’ ‘Yup.’
"In many ways, it showed there was no longer an underground, as such. This proved that there was no longer one society with everyone agreeing how to live . . . The underground had officially come above ground, and consequently no longer existed."
The tunnel goes underground at this point.
London Underground
Use 6 underground when its meaning, tone and grammar fit the full sentence. A synonym is not always a direct replacement.
6 underground means (not comparable) Below the ground; below the surface of the Earth..
Common synonyms include subterranean, hypogean, covered, concealed.
Possible antonyms include mainstream.
There is an underground tunnel that takes you across the river.
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