Day of Atonement (3,6)
I believe the answer is:
yom kippur
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">day of atonement</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for yom kippur that I've seen before include "Annual solemn Jewish Day of Atonement" , "Day of atonement, Jewish festival" , "Holiest fast day of the Jewish calendar" , "Jewish holy day" , "Religious fast" .)