Withdraw, break away (6)
I believe the answer is:
secede
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">withdraw</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >'<span class="explanation-format__original">break away</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for secede that I've seen before include "Break away (politically)" , "Formally achieve independence" , "Withdraw (from organization)" , "Withdraw (from a federal union or organisation)" , "'Withdraw formally, from a political body perhaps (6)'" .)