Second-in-command (6)
I believe the answer is:
deputy
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">second-in-command</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 deputy that I've seen before include "US sheriff's assistant" , "One given the power to act for another" , "Second-in-command" , "The next in command, replaces boss when necessary" , "Person appointed to substitute for another" .)