Fail to develop (8)
I believe the answer is:
stagnate
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fail to develop</span>' is the definition.<br/ ><span class="explanation-format__explanation">(stagnate can mean to fail to develop or go stale)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for stagnate that I've seen before include "Lapse into inactivity" , "Cease to flow or move" , "Cease activity" , "Become dull through inactivity" , "Tan gates could vegetate" .)