Subterranean means lying or happening below the ground. A subterranean chamber, subterranean rivers, subterranean passages.
It is more formal than underground and belongs to archaeology, geology and description. Subterranean rivers are real and London has several buried ones — the Fleet and the Tyburn among them. Figuratively it means hidden and running beneath the surface: subterranean tensions. Note that the Latin is sub plus terra, so it is literally under the earth.
1adjectivesubterraneanLying or happening below the ground.
“The cave divers explored a subterranean river deep beneath the hills.”
Too few real examples of this word to estimate which sense is commonest.
subterranean is a quality of being underground.
Latin subterraneus is sub plus terra, earth. Terrace, terrain and Mediterranean come from the same earth.
Proto-Indo-European
*ters-
English, today
subterranean
From subterrāneus + -an. Compare subterrane and subterraneous.
Etymology from Wiktionary, CC BY-SA