Slight convexity (6)
I believe the answer is:
camber
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">slight convexity</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for camber that I've seen before include "Slight upward curve in road, wing etc" , "Slope on road surface" , "Slight convexity, like the surface of a road" , "Road surface curvature" , "bend in road" .)