When something is declared null and void, it simply means it is canceled or ineffective. Therefore, some antonyms that can be used for the term include "validated," "approved," "authorized," "sanctioned," "ratified," "confirmed," and "legitimate." In essence, these words mean the opposite of null and void, indicating that whatever was previously considered null and void now holds weight and has a genuine existence. Furthermore, by using these antonyms, you can emphasize the importance and significance of what was previously declared null and void, giving your audience a sense of the value of the thing in question.