subterraneity means the quality of being subterranean. Lexicurio rates it Sui generis — a strength score of 100 out of 100.
noun
- The quality of being subterranean.“SUBTERANEITY,^([sic]) a being ſubterraneous.”
- Something that is subterranean.“Every big post office has one. Some have dozens. St. Martin’s-le-Grand is a warren, Mount Pleasant a veritable honeycomb—a positive castle of Otranto with, in place of subterraneities, a hidden, circling passage upon every floor.”