subterranean

About 1.30 uses per million words.

Meaning

1. adjective Below ground, under the earth, underground.
2. adjective Secret, concealed.
3. noun Someone or something that is subterranean.

Similar words

subsurface covert ulterior belowground underground burrowing groundwater fossorial ground geothermal

Often followed by

passage passages water world clover waters chambers chamber and fires

Word family

subterraneanly subterraneous subterraneously