1. Antique building or part of a building below ground, i.e. a cellar, basement, etc.
2. Underground rock-cut or built tomb with niches for cremated remains or loculi for bodies. Smaller than catacombs, it was usually intended for one family or group.
"hypogaeum." A Dictionary of Architecture and Landscape Architecture. . Encyclopedia.com. (October 22, 2018). https://www.encyclopedia.com/education/dictionaries-thesauruses-pictures-and-press-releases/hypogaeum
"hypogaeum." A Dictionary of Architecture and Landscape Architecture. . Retrieved October 22, 2018 from Encyclopedia.com: https://www.encyclopedia.com/education/dictionaries-thesauruses-pictures-and-press-releases/hypogaeum