write-off vs write-down

write-off and write-down both are nouns.

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

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

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

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