cosigner vs cosignatory

cosigner and cosignatory both are nouns.

Word	Noun	Adjective	Verb	Adverb
cosigner	Yes	No	No	No
cosignatory	Yes	Yes	No	No

As nouns, cosigner and cosignatory are synonyms defined as:

cosigner and cosignatory: one of two or more signers of the same document (as a treaty or declaration)

cosigner (noun)	cosignatory (noun)
one of two or more signers of the same document (as a treaty or declaration)	one of two or more signers of the same document (as a treaty or declaration)
a signer in addition to the principal signer (to verify the authenticity of the principal signature or to provide surety)

cosigner (adjective)	cosignatory (adjective)
	signing jointly with others