cupola

American Heritage® Dictionary of the English Language, Fourth Edition

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

Century Dictionary and Cyclopedia

1. n. 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. The Italian word signifies a hemispherical roof which covers a circular building, like the Pantheon at Rome or the temple of Vesta at Tivoli. Most modern cupolas are semi-elliptical, cut through their shortest diameter; but the greater number of ancient cupolas were hemispherical. In colloquial use, the cupola is often considered as a diminutive dome, or the name is specifically applied to a small structure rising above a roof and often having the character of a tower or lantern, and in no sense that of a dome.
2. n. The round top of any structure, as of a furnace; the structure itself. See cupola-furnace. Specifically
3. n. Milit., a revolving shot-proof turret, formed of strong timbers, and armored with massive iron plates. In some systems of cupolas the tower is erected on a base which is made to turn on its center by means of steam-power. Within the turret heavy ordnance is placed, and fired through openings in the sides. Farrow, Mil. Encye.
4. n. In anatomy: The summit of the cochlea. The summit of an intestinal gland.
5. n. In conchology, the so-called dorsal or visceral hump, made by the heap of viscera.

Wiktionary

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

GNU Webster's 1913

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

WordNet 3.0

1. n. a vertical cylindrical furnace for melting iron for casting
2. n. a roof in the form of dome