Corroborate (7)
I believe the answer is:
confirm
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">corroborate</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that corroborate can be written as confirm)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for confirm that I've seen before include "Establish the truth of" , "Corroborate" , "Substantiate" , "Strengthen" , "Provide supporting evidence, make definite" .)