in·dis·pen·sa·ble /ˌin-di-'spen-sə-bəl/ adj: having rights so connected to the claims of the parties to an action that the action cannot be adjudicated without affecting those rights see also indispensable party at party
Merriam-Webster’s Dictionary of Law. Merriam-Webster. 1996.
basic, called for, cardinal, central, compulsory, critical, crucial, dictated, essential, exigent, fundamental, high-priority, imperative, important, imposed, integral, irreplaceable, key, main, major, mandatory, necessarius, necessary, necessitated, needed, obligatory, of importance, pivotal, pressing, primary, required, requisite, significant, unavoidable, urgent, vital, wanted
associated concepts: indispensable evidence, indispensable parties
cardinal (basic), central (essential), compulsory, essential (required), exigent, fundamental, grave (important), imperative, important (urgent), instrumental, integral, mandatory, material (important), necessary (required), necessity, obligatory, requisite, urgent, vital
Burton's Legal Thesaurus. William C. Burton. 2006
The Essential Law Dictionary. — Sphinx Publishing, An imprint of Sourcebooks, Inc. Amy Hackney Blackwell. 2008.