ancillary vs accessory

ancillary is not a noun while accessory is a noun.

Word	Noun	Adjective	Verb	Adverb
ancillary	No	Yes	No	No
accessory	Yes	Yes	No	No

As adjectives, ancillary and accessory are synonyms defined as:

Other synonyms of ancillary include adjunct, adjuvant, appurtenant, auxiliary.

ancillary (noun)	accessory (noun)
	a supplementary component that improves capability
	clothing that is worn or carried, but not part of your main clothing
	someone who helps another person commit a crime

ancillary (adjective)	accessory (adjective)
furnishing added support	furnishing added support
	aiding and abetting in a crime