One seeking retribution (7)
I believe the answer is:
avenger
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">one seeking retribution</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 avenger that I've seen before include "One seeking retribution" , "Someone seeking to settle a score" , "One carries out retribution" , "One settles score" , "person wanting justice through violence?" .)