Gradually diminish (7)
I believe the answer is:
dwindle
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">gradually diminish</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for dwindle that I've seen before include "Degenerate" , "Shrink, grow smaller" , "Become smaller or fewer" , "Diminish gradually" , "Grow less - waste away" .)