Definition of "subterranean"

Again the bearers took up the coffin, and cold and damp the subterranean air came from the opened vault. The tapers were lowered, and shed a ghastly light on the rows of piled coffins, and the moisture glittering on the walls.

1834, L[etitia] E[lizabeth] L[andon], chapter XIX, in Francesca Carrara. […], volume III, London: Richard Bentley, […], (successor to Henry Colburn), page 162

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

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 October 17, Katrin Bennhold, “Fake Polls and Tabloid Coverage on Demand: The Dark Side of Sebastian Kurz”, in The New York Times‎