cancel vs write off

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

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

As verbs, write off is a hyponym of cancel; that is, write off is a word with a more specific, narrower meaning than cancel:

cancel (noun)	write off (noun)
a notation cancelling a previous sharp or flat

cancel (verb)	write off (verb)
make invalid for use	reduce the estimated value of something
remove or make invisible	concede the loss or worthlessness of something or somebody
declare null and void; make ineffective	write something fluently, and without hesitation
postpone indefinitely or annul something that was scheduled	cancel (a debt)
make up for