Polite title (3)
I believe the answer is:
sir
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">polite title</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 sir that I've seen before include "Knight's prefix" , "Title for knight or teacher" , "Respectful address for a man" , "Honorary male title" , "Formal term of address" .)