Soft cheese fly must abandon shortly (4)
I believe the answer is:
brie
'soft cheese' is the definition.
(brie is a soft cheese)
'fly must abandon shortly' is the wordplay.
'must abandon' suggests deleting specific letters.
'shortly' becomes 'briefly'.
'briefly' with 'fly' removed is 'BRIE'.
(Other definitions for brie that I've seen before include "Bergamot-flavoured tea" , "Variety of cheese" , "cheese-producing region" , "Kind of soft cheese" , "Food" .)