Fan in sudden disappointment (4)
I believe the answer is:
blow
This clue is a double definition.
'fan' is the first definition.
(thesaurus)
'sudden disappointment' is the second definition.
(I've seen this before)
'in' acts as a link.
(Other definitions for blow that I've seen before include "Setback" , "Be windy; unlucky stroke" , "Sudden shock, wind" , "Whistle - hit" , "Waste" .)