noun
or hy·po·gae·um ˌ ̷ ̷ ̷ ̷ at hypo- +ˈjēəm
( plural hypo·gea or hypo·gaea -ēə)
Etymology: Latin, from Greek hypogeion, hypogaion, from neuter of hypogeios, hypogaios subterranean, from hypo- + gē, gaia earth, ground
1.
a. : the subterranean part of an ancient building : cellar
b. : the underground service galleries of an ancient amphitheater
2. : an ancient underground burial chamber or series of such rooms : catacomb