Crush fly (4)
I believe the answer is:
dash
This clue is a double definition.
'crush' is the first definition.
(thesaurus)
'fly' is the second definition.
(I've seen this before)
(Other definitions for dash that I've seen before include "Hurry; destroy (hopes)" , "Vivacity" , "Hurry ("must ____!")" , "style" , "zip" .)