subterraneous

adj

1. (not-comparable)Subterranean.

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

   “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.”

   “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.”

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