"In a perfect world . . ." (7)
I believe the answer is:
ideally
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">in a perfect world</span>' is the definition.<br/ ><span class="explanation-format__explanation">(in an ideal world)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ideally that I've seen before include "In the best possible way or circumstances" , "In the best of all possible worlds" , "for preference" , "In the most perfect way" , "In perfect circumstances" .)