Be sick (3)
I believe the answer is:
ail
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">be sick</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ail that I've seen before include "Be unwell, suffer" , "upset" , "distress" , "Be ill or unwell" , "Be unwell, feel poorly" .)