Definition of "subterraneous"

[S]he recollected a ſubterraneous paſſage which led from the vaults of the caſtle to the church of St. Nicholas.

1764 December 24 (indicated as 1765), Onuphrio Muralto, translated by William Marshal [pseudonyms; Horace Walpole], chapter I, in The Castle of Otranto, […], London: […] Tho[mas] Lownds […], page 22

The Indians of the Orellanna, also, tell of horrible noises heard occasionally in the Paraguaxo, […] Others have endeavored to account for these discharges of "mountain artillery" on humbler principles; attributing them […] to the disengagement of hydrogen, produced by subterraneous beds of coal in a state of ignition.

1836 October, Washington Irving, chapter XXVI, in Astoria, or Anecdotes of an Enterprise beyond the Rocky Mountains. […], volume I, Philadelphia, Pa.: [Henry Charles] Carey, [Isaac] Lea, & Blanchard, page 254

A low rumbling sound was heard; a subterraneous hum; and then all held their breaths; as bedraggled with trailing ropes, and harpoons, and lances, a vast form shot lengthwise, but obliquely from the sea.

1851 November 14, Herman Melville, Moby-Dick; or, The Whale, 1st American edition, New York, N.Y.: Harper & Brothers; London: Richard Bentley

The 3-mile underground railway—or "subterraneous wagonway"—was begun about 1770 by Christopher Bedlington, and was therefore commonly known as Kitty's Drift.

1944 September and October, Charles E. Lee, “An Ancient Underground Railway”, in Railway Magazine, page 275