Lacking slack (4)
I believe the answer is:
taut
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">lacking slack</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for taut that I've seen before include "Fully stretched" , "Stretched, pulled tight" , "On the slope" , "Tense, stretched tight" , "Held in tension" .)