Duty or burden (4)
I believe the answer is:
onus
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">duty</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">burden</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for onus that I've seen before include "albatross?" , "Obligation - charge" , "Encumbrance" , "Capulet opponent (R&J)" , "'Responsibility, task or burden (4)'" .)