write-down vs write-off

write-down and write-off both are nouns.

Word	Noun	Adjective	Verb	Adverb
write-down	Yes	No	No	No
write-off	Yes	No	No	No

As nouns, write-down and write-off are synonyms defined as:

write-down and write-off: (accounting) reduction in the book value of an asset

write-down (noun)	write-off (noun)
(accounting) reduction in the book value of an asset	the act of cancelling from an account a bad debt or a worthless asset
	(accounting) reduction in the book value of an asset