Suds, froth (4)
I believe the answer is:
foam
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">suds</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >'<span class="explanation-format__original">froth</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for foam that I've seen before include "Suds" , "Fizz, froth" , "Mass of small bubbles" , "Boiling bubbles" , "Suspension of gas in a liquid" .)