Curving inwards (7)

I believe the answer is:
concave
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">curving inwards</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 concave that I've seen before include "Bending inwards" , "Hollow" , "Curving inward" , "Curving inwards" , "Curved inwards" .)