Of small width (6)
I believe the answer is:
narrow
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">of small width</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for narrow that I've seen before include "Keen" , "Lacking tolerance" , "Straight or tight" , "Strait or confined" , "Slender - spare" .)