The term "co-sign" typically refers to the act of signing a document or agreement along with another person, usually for the purpose of assuming joint responsibility for a particular obligation. Antonyms for co-sign might include sign individually, decline to sign, or refuse to co-sign. If someone declines to co-sign, they are essentially indicating that they do not wish to become involved in the agreement or assume joint responsibility for the obligation at hand. In contrast, if someone signs the document individually, they are taking sole responsibility for the agreement without the need for a co-signer. Refusing to co-sign can be a way to avoid potential liability or simply to maintain one's independence and autonomy in a relationship or business transaction.