expense vs write off

expense is a noun but write off is not a noun.

Word	Noun	Adjective	Verb	Adverb
expense	Yes	No	Yes	No
write off	No	No	Yes	No

As verbs, expense and write off are synonyms defined as:

Other synonyms of expense include write down.

expense (noun)	write off (noun)
a detriment or sacrifice
amounts paid for goods and services that may be currently tax deductible (as opposed to capital expenditures)
money spent to perform work and usually reimbursed by an employer

expense (verb)	write off (verb)
reduce the estimated value of something	reduce the estimated value of something
	concede the loss or worthlessness of something or somebody
	write something fluently, and without hesitation
	cancel (a debt)