Record decisive win finally for white (7)
I believe the answer is:
albumen
'white' is the definition.
(I've seen this before)
'record decisive win finally' is the wordplay.
'record' becomes 'album' (I've seen this before).
'finally' suggests the final letters.
The final letters of 'decisive win' are 'en'.
'album'+'en'='ALBUMEN'
'for' is the link.
(Other definitions for albumen that I've seen before include "Egg-white" , "Egg's white" , "White poacher" , "The white part of an egg" .)