The word 'subterranean' is often used when talking about natural or man-made objects below the Earth's surface. Engineers are concerned about the subterranean water levels affecting the building's foundation.
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Physical Realm Focus
'Subterranean' specifically denotes things not visible on the surface, especially related to geography and structures. Subterranean tunnels provided the miners access to the coal seams.
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Not For People
While 'subterranean' often describes places, it's not typically used to describe people or animals. The documentary highlighted the subterranean habitats of various insects.