Sworn promise (4)
I believe the answer is:
oath
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sworn promise</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 oath that I've seen before include "Solemn vow" , "What frustrated people say" , "swearing" , "Commitment to tell the truth" , "Curse - sworn statement" .)