To sign a credit agreement with someone and agree to share the debt with that person or assume the debt if the other person defaults, that is, doesn't pay
To endorse the loan application of another person who might otherwise be denied a loan Co-signors are responsible for loan payments if the principal applicant is unable to repay the loan
To accept joint responsibility for repaying someone else's loan If the borrower doesn't make loan payments, the co-signer is liable for the debt
{f} sign jointly, sign as a cosigner, sign a document along with other signers; endorse the signature of another person (as promissory note or for a loan)