Wordnet 3.0
NOUN (2)
1.
one of two or more signers of the same document (as a treaty or declaration);
[syn: cosigner, cosignatory]
2. a signer in addition to the principal signer (to verify the authenticity of the principal signature or to provide surety);
WordNet (r) 3.0 (2006):
cosigner
n 1: one of two or more signers of the same document (as a
treaty or declaration) [syn: cosigner, cosignatory]
2: a signer in addition to the principal signer (to verify the
authenticity of the principal signature or to provide surety)