Rely (upon) (6)
I believe the answer is:
depend
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">rely upon</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 depend that I've seen before include "Rest" , "Put trust (in)" , "Count on or hang from" , "Rely (upon)" , "Hang down or be connected to something" .)