Cupola (4)
I believe the answer is:
dome
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">cupola</span>' is the definition.<br/ ><span class="explanation-format__explanation">(architectural term)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for dome that I've seen before include "Rounded vault of a roof" , "Mode or arched roof" , "Head" , "Hemispherical roof" , "Crown" .)