cupola

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A vaulted roof or ceiling.
• noun A small dome set on a circular or polygonal base or resting on pillars.
• noun A domelike structure surmounting a roof or dome, often used as a lookout or to admit light and air.
• noun A cylindrical shaft type of blast furnace used for remelting metals, usually iron, before casting.
• noun A small rounded and domed structure, as for observation, on a tracked, armored vehicle.

from The Century Dictionary.

• noun In architecture, a vault, either hemispherical or produced by the revolution about its axis of two curves intersecting at the apex, or by a semi-ellipse covering a circular or polygonal area, and supported either upon four arches or upon solid walls.
• noun The round top of any structure, as of a furnace; the structure itself. See cupola-furnace. Specifically
• noun Milit., a revolving shot-proof turret, formed of strong timbers, and armored with massive iron plates.
• noun In anatomy: The summit of the cochlea. The summit of an intestinal gland.
• noun In conchology, the so-called dorsal or visceral hump, made by the heap of viscera.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Arch.) 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.
• noun A small structure standing on the top of a dome; a lantern.
• noun A furnace for melting iron or other metals in large quantity, -- used chiefly in foundries and steel works.
• noun A revolving shot-proof turret for heavy ordnance.
• noun (Anat.) The top of the spire of the cochlea of the ear.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun architecture A dome-shaped ornamental structure located on top of a larger roof or dome.
• noun military A small turret, usually on a hatch of an armoured fighting vehicle.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a vertical cylindrical furnace for melting iron for casting
• noun a roof in the form of a dome