Synonyms and related words :
absolute, aground, authoritative, binding, canonical, compulsory, conclusive, decisive, decretory, dictated, didactic, entailed, final, formulary, hard-and-fast, imperative, imposed, instructive, irrevocable, mandated, mandatory, must, obligatory, official, on the rocks, peremptory, preceptive, prescribed, prescript, prescriptive, regulation, required, rubric, standard, statutory, ultimate, without appeal