Irish moss (9)
I believe the answer is:
carrageen
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">irish moss</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for carrageen that I've seen before include "Irish moss" , "Edible red seaweed" , "Purplish-red, edible seaweed" .)