Harmony or agreement (6)
I believe the answer is:
unison
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">harmony</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that unison is a type of accord)</span><br/ ><br/ >'<span class="explanation-format__original">agreement</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that unison is a type of agreement)</span><br/ ><br/ ></span>
(Other definitions for unison that I've seen before include "There's agreement" , "Sameness in pitch" , "All singing the same notes" , "Concordance" , "Simultaneous utterance" .)