The word "cosigning" refers to the act of signing a document or loan agreement alongside another person as a guarantee of payment or performance. There are various antonyms for the word "cosigning" that denote opposite meanings or actions. One antonym is "disavowing," which means to deny knowledge or responsibility for something. Another antonym is "rejecting," which means to refuse or decline an offer or proposal. "Abdicating" is also an antonym of cosigning, which means to renounce or give up a responsibility or position of authority. Lastly, "disowning" is another antonym for cosigning, which means to repudiate or disclaim ownership or affiliation.