Sharp side of a blade (4)
I believe the answer is:
edge
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sharp side of a blade</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 edge that I've seen before include "Rim, lip" , "Move slowly" , "'Border, boundary, rim (4)'" , "Sharpened side of blade" , "Rim - move gradually" .)