(a.) Morally or legally binding; mandatory; imperative; as, obedience is obligatory on a soldier\; imposing duty or obligation; requiring performance or forbearance of some act; -- often followed by on or upon.

absolute binding choiceless compulsory conclusive de rigueur decisive decretory demanded dictated entailed essential exigent final hard-and-fast imperative imperious importunate imposed incumbent indispensable inevitable involuntary irrevocable mandated mandatory must necessary necessitous peremptory prescript prescriptive required requisite ultimate urgent without appeal without choice