write down vs write-down

write down is not a noun while write-down is a noun.

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

write down (noun)	write-down (noun)
	(accounting) reduction in the book value of an asset

write down (verb)	write-down (verb)
reduce the estimated value of something
put down in writing; of texts, musical compositions, etc.