29 synonyms for necessary such as fated, called for, certain, and destined. Necessary is an adjective, and its antonyms are unnecessary, non-essential, and dispensable.
Called for, compulsory, de rigueur, demanded, essential, imperative, incumbent, indispensable, mandatory, needed, needful, obligatory, of the essence, required, requisite, and vital.
Certain, destined, fated, ineluctable, inescapable, inevitable, inexorable, predestined, predetermined, preordained, sure, and unavoidable.