Impetuous, spontaneous (9)
I believe the answer is:
impulsive
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">impetuous</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that impetuous can be written as impulsive)</span><br/ ><br/ >'<span class="explanation-format__original">spontaneous</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ ></span>
(Other definitions for impulsive that I've seen before include "Done without forethought" , "Rash" , "Spontaneous" , "Acting without forethought" , "responding promptly" .)