1. All the parts of a building beneath the level of the ground.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• hypogeic,
• Hypogein,
• Hypogeen,
• hypogeuos,
• hypogeous,
• Hypogaous,
• gypogeum,
• bypogeum,
• nypogeum,
• jypogeum,
• uypogeum,
• yypogeum,
• htpogeum,
• hgpogeum,
• hhpogeum,
• hypogheum,
• Hypoceum,
• Lypogram,
• hypogonus,
• hypnogenus

The plural of the "Hypogeum" can be the "hypogea".

The singular of the "Hypogeum" can be the "Hypogeum".