Breathe with difficulty (6)
I believe the answer is:
wheeze
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">breathe with difficulty</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for wheeze that I've seen before include "Breathe noisily; scheme" , "Breathe with hoarse whistling sound" , "A heavy breath or jolly jape" , "Clever scheme or noisy breath" , "Audible inspiration" .)