co-maker

noun | \ ˈkō-ˌmā-kər \ | co-mak·er

1. : one of two or more persons who sign an instrument to indicate a promise to pay a financial obligation

   Note: Any co-maker may be sued for the entire amount of the indebtedness, although a co-maker who is forced to pay more than his or her share may seek contribution from the other co-makers.