When something is "rendered null and void," it means it is no longer valid or effective. Some antonyms for this phrase may include "valid," "effective," "binding," "enforceable," "legitimate," or "operative." These terms imply that whatever was previously null and void is now functional and able to serve its intended purpose. Another set of antonyms could be "confirmed," "approved," "ratified," "sanctioned," or "endorsed." These words suggest that the previous invalidity of a document, decision, or action has been rectified or approved, and it is now accepted and recognized as valid. Choosing the appropriate antonyms depends on the context and intended meaning.