subterranean

Etymology

Borrowed from Latin subterrāneus.

adj

1. Below ground, under the earth, underground.
   And you were in the parking lot / Subterranean by your own design 1975, Joni Mitchell (lyrics and music), “The Boho Dance”, in The Hissing of Summer Lawns
   This is a story of north-south connection, and it begins with the fact that late in 1863 the Great Northern Railway completed a subterranean connection from its terminus at King's Cross to the tracks of the Metropolitan enabling the Great Northern to run through to the Met's easterly terminus at Farringdon Street. 2012, Andrew Martin, Underground Overground: A passenger's history of the Tube, Profile Books, page 52
   The best way to neutralise its [nuclear waste's] threat is to move it into a subterranean vault, of the kind the UK plans to build later this century. Once interred, the waste will be left alone for tens of thousands of years, while its radioactivity cools. December 15 2022, Samanth Subramanian, “Dismantling Sellafield: the epic task of shutting down a nuclear site”, in The Guardian
2. (by extension) Secret, concealed.
   The subterranean tool of buying rigged opinion polling and media coverage is outlined in remarkable detail in chat exchanges recovered from the cellphone of one of Mr. Kurz’s closest allies and friends, Thomas Schmid. 2021-10-17, Katrin Bennhold, “Fake Polls and Tabloid Coverage on Demand: The Dark Side of Sebastian Kurz”, in The New York Times, →ISSN