Source : Webster's Revised Unabridged Dictionary (1913)

Subterranean \Sub`ter*ra"ne*an\, Subterraneous
\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.