cosign vs cosigner

cosign is not a noun while cosigner is a noun.

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

cosign (noun)	cosigner (noun)
	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)

cosign (verb)	cosigner (verb)
sign and endorse (another person's signature), as for a loan
sign jointly