The word cosignatory refers to someone who signs a document or contract alongside another person. However, there are several antonyms for this term, which denote different meanings. The first antonym for cosignatory is solitary, which means someone who stands alone in signing a document or taking a decision. Another antonym for cosignatory is unconnected, which implies that the person signing the document has no relationship with the primary signatory. Similarly, the words "unrelated" and "unassociated" are also possible antonyms for cosignatory, indicating a lack of connection or association with the primary signer. Finally, the word "nonparticipant" refers to someone who does not sign a contract or document at all, making it the direct opposite of cosignatory.