Clerk (6)
I believe the answer is:
teller
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">clerk</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 teller that I've seen before include "One who instructs" , "who worked on the hydrogen bomb" , "One records cash" , "one gives relation" , "One introducing relation" .)