Polite form of address (3)
I believe the answer is:
sir
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">polite form of address</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 sir that I've seen before include "Feted fellow" , "Form of address for a knight" , "Way to address gentleman" , "Gentleman's form of address" , "Polite form of address to a man" .)