I (inescapable) adjective avoidless, certain, choiceless, compelling, constraining, decided, decreed, designated, destined, expected, fated, fateful, fixed, foreordained, imminent, impending, ineluctable, includible, inevitable, inexorable, irresistible, irrevocable, ordained, sealed, settled, sure, unalterable, unavoidable, uncontrollable, undeniable, unevasible, unpreventable associated concepts: necessary damages, necessary expenses, necessary implication, necessary inference, necessary injury II (required) adjective all-important, basic, binding, bounden, chief, coercive, compelling, compulsory, critical, crucial, demanded, dictated, essential, exigent, expedient, fundamental, imperative, important, imposed, incumbent, indispensable, integral, key, mandatory, necessitated, necessitous, needed, obligatory, paramount, prerequisite, prescribed, prime, principal, requisite, requisitioned, significant, strategic, strategical, substantive, urgent, vital associated concepts: necessary parties III noun essence, essential, essentiality, indispensable thing, necessitas, necessities, necessitousness, necessitude, necessity, need, prerequirement, prerequisite, qualification, requirement, requisite, vitals associated concepts: duty to provide necessaries, necessaries of life IV index binding, cardinal (basic), central (essential), compelling, compulsory, desideratum, essential (required), exigent, fundamental, imperative, important (urgent), indispensable, integral, mandatory, material (important), need (requirement), obligatory, peremptory (imperative), primary, requisite, unavoidable (inevitable), urgent

Burton's Legal Thesaurus. . 2006

Required; needed; essential.

The Essential Law Dictionary. — Sphinx Publishing, An imprint of Sourcebooks, Inc. . 2008.

adj., adv.
   1) essential.
   2) less forcefully, it can mean convenient, useful or making good sense.

Law dictionary. . 2013.