All-important (7)
I believe the answer is:
crucial
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">all-important</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for crucial that I've seen before include "Pivotal" , "Decisive - very important" , "Of critical importance, decisive" , "Of immediate importance" , "Of utmost importance" .)