Write-off (4)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
loss
'write-off' is the definition.
(financial loss)
This is all the clue.
(Other definitions for loss that I've seen before include "Red figures on a balance sheet or ledger" , "Disadvantage" , "Cost" , "sacrifice?" , "Destruction" .)