Common mixer (5)
I believe the answer is:
tonic
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">common mixer</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 tonic that I've seen before include "something nice and fresh" , "Keynote of a scale" , "Small drink of spirits" , "Carbonated mixer" , "Gin mixer - pick-me-up" .)