Grow tense (7)
I believe the answer is:
tighten
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">grow tense</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 tighten that I've seen before include "Make more taut" , "Restrict" , "Stiffen" , "Become more tense" , "Make stricter" .)