Cosigned means to sign a document with someone else, usually as a guarantee for repayment or reliability. It is often used in financial matters or loan applications. The antonyms of cosigned are disavow, disapprove, deny, dissociate, and disown. Disavow means to deny any connection with someone or something. Disapprove means to have a negative opinion about a person or something. Deny means to declare that a statement or action is untrue. Dissociate means to separate oneself from a group, organization, or person. Disown means to reject a person or thing that one is closely associated with. All these antonyms imply a lack of responsibility or involvement in a particular matter.