The meaning that defines the word "subterranean" is below ground.
The correct meaning that defines the word "subterranean" is "below ground." To determine the meaning of a word, you can consult a reliable dictionary. One widely used online dictionary is Merriam-Webster. By searching for the word "subterranean" in this dictionary, you can find its definition and different meanings. In this case, the definition of "subterranean" will indicate that it refers to something that is below or beneath the surface of the earth.
