Assurance (9)
I believe the answer is:
certainty
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">assurance</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for certainty that I've seen before include "Sure thing" , "A definite fact" , "Banker" , "State of being sure" , "Foregone conclusion" .)