Gracefully slender (6)
I believe the answer is:
svelte
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">gracefully slender</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 svelte that I've seen before include "free" , "Sylphlike" , "Elegant and of slender build" , "Gracefully slim" , "Attractively slim" .)