Subterranean

{ Sub′ter‐ra″ne‐an (?), Sub′ter‐ra″ne‐ous (?), } a. [L. subterraneus; sub under + terra earth. See Terrace.] Being or lying under the surface of the earth; situated within the earth, or under ground; as, subterranean springs; a subterraneous passage. — Sub′ter‐ra″ne‐ous‐ly, adv.