Cupola

Definition:

(n.) A roof having a rounded form, hemispherical or nearly so; also, a ceiling having the same form. When on a large scale it is usually called dome.
(n.) A small structure standing on the top of a dome; a lantern.
(n.) A furnace for melting iron or other metals in large quantity, -- used chiefly in foundries and steel works.
(n.) A revolving shot-proof turret for heavy ordnance.
(n.) The top of the spire of the cochlea of the ear.

Compare cupola with other words:

cupola vs. tower