Milfoil (6)
I believe the answer is:
yarrow
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">milfoil</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for yarrow that I've seen before include "Flowering plant" , "Creeping perennial plant, used in herbal medicine" , "'Achillea millefolium'" , "bloomer" , "Species of milfoil" .)