Lewis & Short

hypŏgaeum, i, v. hypogeum.

hypŏgēus, a, um, adj., = ὑπόγαιος, underground: loca, Cael. Aur. Tard. 2, 37, 191.
Hence, subst.: hypŏgēum or hy-pŏgaeum, i, n., = ὑπόγειον (ὑπόγαιον), a vault or cellar under ground, Vitr. 6, 11; a burying-vault, sepulchre, Petr. 111, 2; Inscr. Grut. 1114, 3.