cu·po·la 
(kypə-lə)
(kypə-lə)n.
1. Architecture
a. A vaulted roof or ceiling.
b. A small dome set on a circular or polygonal base or resting on pillars.
c. A small structure surmounting a roof or dome, often used as a lookout or to admit light and air.
2. A cylindrical shaft type of blast furnace used for remelting metals, usually iron, before casting.
3. A small rounded and domed structure, as for observation, on a tracked, armored vehicle.
[Italian, from Late Latin cūpula, diminutive of Latin cūpa, tub; possibly akin to various words denoting hollow objects across Eurasia, such as Greek kupellon, drinking vessel, goblet, Old Norse húfr, hull of a ship, Old English hȳf, skep, and Sanskrit kūpaḥ, hole.]
cupo·laed (kypə-ləd) adj.
cupola