Decisive, critical (7)
I believe the answer is:
crucial
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">decisive</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(associated in meaning)</span><br/ ><br/ >'<span class="explanation-format__original">critical</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(associated in meaning)</span><br/ ><br/ ></span>
(Other definitions for crucial that I've seen before include "Pivotal" , "All-important" , "Of utmost importance" , "Of extreme importance" , "'Decisive, critical (7)'" .)