Not accustomed (to) (6)
I believe the answer is:
unused
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">not accustomed to</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for unused that I've seen before include "Surplus" , "In mint condition" , "idle" , "factory fresh" , "Left over" .)