Be indisposed (3)
I believe the answer is:
ail
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">be indisposed</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ail that I've seen before include "distress" , "upset" , "Trouble, afflict; be sickly" , "Become unwell" , "Cause to feel indisposed" .)