Burden, duty (4)
I believe the answer is:
onus
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">burden</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >'<span class="explanation-format__original">duty</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ ></span>
(Other definitions for onus that I've seen before include "Duty or responsibility" , "Responsibilty" , "'Responsibility, task or burden (4)'" , "Burden, duty" , "'Burden, load (4)'" .)