Expiring (5)
I believe the answer is:
dying
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">expiring</span>' is the definition.<br/ ><span class="explanation-format__explanation">('die' can be a synonym of 'expire')</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for dying that I've seen before include "Perishing" , "Ceasing to function" , "On one's last legs" , "Near death" , "On the point of death" .)