hy·po·ge·um 
(hī′pə-jēəm)
(hī′pə-jēəm)n. pl. hy·po·ge·a (-jēə)
1. A subterranean chamber of an ancient building.
2. An ancient subterranean burial chamber, such as a catacomb.
[Latin hypogēum, from Greek hupogeion, from neuter of hupogeios, underground; see HYPOGEAL.]