Pledge — guarantee (6)
I believe the answer is:
surety
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">pledge</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that surety is a type of guarantee)</span><br/ ><br/ >'<span class="explanation-format__original">guarantee</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that surety is a type of guarantee)</span><br/ ><br/ ></span>
(Other definitions for surety that I've seen before include "Money given as guarantee of action" , "Legal safeguard against loss" , "Semitic language" , "Safeguard given against financial loss" , "Guarantee (for pledge)" .)