Synonyms and related words :
absolute, binding, choiceless, coactive, compelling, compulsatory, compulsive, conclusive, constraining, decisive, decretory, dictated, driving, entailed, exigent, final, hard-and-fast, imperative, imperious, importunate, imposed, inevitable, involuntary, irresistible, irrevocable, mandated, mandatory, must, necessary, necessitous, obligatory, peremptory, prescript, prescriptive, pressing, required, restraining, ultimate, urgent, without appeal, without choice