Trading centre (4)
I believe the answer is:
mart
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">trading centre</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 mart that I've seen before include "Trading centre" , "Take tram to market" , "US shop; market" , "Place" .)