onion dome

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

• noun A pointed bulbous domelike roof, used especially in parts of Russia and eastern Europe.

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

• noun (Architecture) A dome with a pointed top, its width often extending beyond the width of the tower it covers; -- a style of architecture characteristic of Russian Orthodox churches.

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

• noun architecture An onion-shaped dome, characteristic of august buildings in Moghul and Russian architecture

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

• noun a dome that is shaped like a bulb; characteristic of Russian and Byzantine church architecture