Change gradually (6)
I believe the answer is:
evolve
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">change gradually</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 evolve that I've seen before include "Unravel" , "Unfold" , "Develop by natural selection" , "Gradually acquire new characteristics" , "Reveal a secret" .)