Sickly (6)
I believe the answer is:
ailing
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sickly</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ailing that I've seen before include "Troubled in mind or body" , "Unwell, in poor condition" , "Sickly, poorly" , "In poor health" , "Suffering" .)