Kind of arch (4)
I believe the answer is:
ogee
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">kind of arch</span>' is the definition.<br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ogee that I've seen before include "Leer" , "S-shaped line" , "S-shaped moulding" , "architectural feature" , "bit of Gothic architecture?" .)