Rotunda

n.

1.

(Arch.) A round building; especially, one that is round both on the outside and inside, like the Pantheon at Rome. Less properly, but very commonly, used for a large round room; as, the rotunda of the Capitol at Washington.

Noun	1.	rotunda - a building having a circular plan and a dome
	2.	rotunda - a large circular room

building, edifice