Antonyms for "declare invalid" include "validate," "approve," "endorse," "ratify," "confirm," "authorize," "legitimize," and "sanction." When something is declared invalid, it means that it is not legally binding or enforceable. Antonyms for this term suggest that the act or decision has been acknowledged as valid or legitimate. The opposite of declaring something invalid is to give it legal or authoritative recognition. This term is often used in legal proceedings or bureaucratic contexts where official approvals or authorizations are necessary. Antonyms of "declare invalid" imply clear-cut decision-making that reflects legitimacy, acceptance, and respect for due process.