Complete agreement (6)
I believe the answer is:
unison
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">complete agreement</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 unison that I've seen before include "All acting the same way at the same time" , "Concord; a trade union" , "All singing the same notes" , "Total agreement or concord" , "Concord, sounding or singing together" .)