Wordnet 3.0
NOUN (1)
1.
a dome that is shaped like a bulb;
characteristic of Russian and Byzantine church architecture;
The Collaborative International Dictionary of English v.0.48:
onion dome \on`ion dome"\, n. (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.
[PJC]
WordNet (r) 3.0 (2006):
onion dome
n 1: a dome that is shaped like a bulb; characteristic of
Russian and Byzantine church architecture