Keep at it (9)
I believe the answer is:
persevere
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">keep at it</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for persevere that I've seen before include "Go on in spite of setbacks" , "hold on" , "Continue despite difficulties" , "Persist steadily" , "Continue in adversity" .)