Not wide (6)
I believe the answer is:
narrow
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">not wide</span>' is the definition.<br/ ><span class="explanation-format__explanation">('narrow' is the opposite to 'wide')</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for narrow that I've seen before include "Short of breadth" , "Strait; close" , "Cramped" , "Meagre, confined" , "With sides close together" .)