Burden of proof (4)
I believe the answer is:
onus
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">burden of proof</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for onus that I've seen before include "Obligation - charge" , "Responsibilty" , "Liability" , "Duty or responsibility" , "Encumbrance" .)