Fly high (4)
I believe the answer is:
soar
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fly high</span>' is the definition.<br/ ><span class="explanation-format__explanation">(soar up into the air)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for soar that I've seen before include "Fly high, Leicester river" , "Significant rise" , "take to the air" , "Rise high into the air" , "Fly high into the air" .)