Cheerful, optimistic (6)
I believe the answer is:
upbeat
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">cheerful</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that cheerful can be written as upbeat)</span><br/ ><br/ >'<span class="explanation-format__original">optimistic</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ ></span>
(Other definitions for upbeat that I've seen before include "maestro communicates this to orchestra" , "Optimistic (colloq.)" , "Promising" , "Cheerful and encouraging, like lively music" , "Relentlessly optimistic" .)