The Oxford Thesaurus An A-Z Dictionary of Synonyms - necessary adj.

1) indispensable, essential, required, needed, compulsory, requisite, vital, demanded, imperative, obligatory, needful, of the essence, important, of the utmost importance, top-priority, high-priority, urgent, exigent, compelling, life-and-death or life-or-death: A good diet is necessary for good health. It is necessary that you come at once. Take the necessary steps to get the job done. 2) inevitable, unavoidable, inescapable, ineluctable: In the circumstances, we find it necessary to ask for your resignation. 3) sure, certain, predetermined, predestined, fated, inexorable; resulting, resultant: The necessary outcome of the affair was that the child was returned to her natural parents. --n. 4) See necessity, 1, below.