Lacking fizz (4)
I believe the answer is:
flat
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">lacking fizz</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for flat that I've seen before include "Even - somewhere to live" , "Apartment - below the note" , "razed to the ground, having had blow-out" , "Boring - apartment" , "without qualification" .)