Trefoil (6)
I believe the answer is:
clover
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">trefoil</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for clover that I've seen before include "A four-leafed one is lucky" , "Weed or forage plant (which it's good to be in)" , "Meadow plant" , "A 19 down" , "Another trefoil, sometimes with lucky four leaves" .)