Fish; heather (4)
I believe the answer is:
ling
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">fish</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(ling is a kind of fish)</span><br/ ><br/ >'<span class="explanation-format__original">heather</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for ling that I've seen before include "Swimmer" , "Fish of the cod family" , "Heather - fish" , "Burbot" , "Cod-like fish" .)