Nun (6)
I believe the answer is:
sister
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">nun</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that nun can be written as sister)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for sister that I've seen before include "'Nurse, nun or relative (6)'" , "trade union member?" , "A kinswoman" , "Member of family" , "Nurse, nun and sibling" .)