Not high (3)
I believe the answer is:
low
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">not high</span>' is the definition.<br/ ><span class="explanation-format__explanation">('low' is the opposite to 'high')</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for low that I've seen before include "Unimportant sort of owl" , "Opposite of high" , "Deep sound of cattle - not high" , "Not high or loud" , "something from Guernsey?" .)