In architecture a vault, usually circular at the base and rising above the central part of a building. Domes come in a wide variety of forms, including saucer-shaped, onion-shaped, pumpkin-shaped, bulbous, parabolic, and hemispheric. A dome can be elevated by being placed on top of a circular or polygonal drum. 

Mirak Mirza Ghiyath. Dome of the Tomb of Humayun, Delhi, India. 1526-1571.