The term "under sign" means to be signed or designated by someone in authority or a higher position. The antonyms for this phrase are "unsigned," "unapproved," "denied," "rejected," or "refused." These words refer to disapproval or a lack of authorization for a particular action or document. When something is denied or refused, it means that it has been rejected and cannot move forward, leading to a possible delay or change in plans. Similarly, when something is unsigned or unapproved, it means that it has not been authorized or acknowledged, and may not have the same level of credibility or authority as something that has been under-signed.