Small dome (6)

I believe the answer is:
cupola
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">small dome</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for cupola that I've seen before include "Round domed roof" , "Domed ceiling" , "Rounded dome" , "Small dome on a roof" , "fireplace" .)