Sudden disappointment (4)
I believe the answer is:
blow
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sudden disappointment</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for blow that I've seen before include "Strong current of air" , "Whistle - hit" , "'..., ..., thou winter wind' (As You Like It)" , "cocaine from US" , "Sudden disappointment" .)