The Collaborative International Dictionary of English v.0.48:

Cupola \Cu"po*la\ (k?"p?-l?), n.; pl. Cupolas (-l?z). [It.
   cupola, LL. cupula, cuppula (cf. L. cupula little tub). fr.
   cupa, cuppa, cup; cf. L. cupa tub. So called on account of
   its resemblance to a cup turned over. See Cup, and cf.
   Cupule.]
   1. (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.
      [1913 Webster]

   2. A small structure standing on the top of a dome; a
      lantern.
      [1913 Webster]

   3. A furnace for melting iron or other metals in large
      quantity, -- used chiefly in foundries and steel works.
      [1913 Webster]

   4. A revolving shot-proof turret for heavy ordnance.
      [1913 Webster]

   5. (Anat.) The top of the spire of the cochlea of the ear.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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

Moby Thesaurus II by Grady Ward, 1.0:

59 Moby Thesaurus words for "cupola":
   antenna tower, apse, arcade, arcature, arch, arched roof, archway,
   barbican, belfry, bell tower, camber, campanile, ceilinged roof,
   colossus, column, concameration, concha, cove, derrick, dome,
   fire tower, geodesic dome, igloo, keystone, lantern, lighthouse,
   martello, martello tower, mast, minaret, monument, obelisk,
   observation tower, ogive, pagoda, pilaster, pillar, pinnacle, pole,
   pylon, pyramid, shaft, skewback, skyscraper, span, spire,
   standpipe, steeple, stupa, television mast, tope, tour, tower,
   turret, vault, vaulting, voussoir, water tower, windmill tower