Bro's sibling (3)
I believe the answer is:
sis
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">bro's sibling</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 sis that I've seen before include "relative" , "Little sibling" , "Family member (informal)" , "Secret Intelligence Service (abbr.)" , "spies ..." .)