D defs.my
Entry 1 sense Webster, 1913

onion dome

/ŭn'-yən dōm/ · on·ion dome · IPA
01 n. A dome with a pointed top, its width often extending beyond the width of the tower it covers; -- a style of architecture characteristic of …
  1. 1.
    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.(Architecture)