Most optimistic (7)
I believe the answer is:
rosiest
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">most optimistic</span>' is the definition.<br/ ><span class="explanation-format__explanation">('rosy' can be similar in meaning to 'optimistic')</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for rosiest that I've seen before include "Most healthy" , "(Of future) most promising; maximally pink" , "Most glowing" , "Most optimistic - stories (anag)" .)