Appurtenance (7)
I believe the answer is:
adjunct
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">appurtenance</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for adjunct that I've seen before include "Incidental extra" , "'Assistant, professor say (7)'" , "Something attached but not essential" , "Thing added" , "Something added, but not essential" .)