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

1) indispensable, necessary, requisite, required, important, imperative, vital, material, quintessential: A strong defence is essential to peace. 2) fundamental, basic, intrinsic, elemental, elementary, principal, primary, key, main, leading, chief: Yeast or baking powder is an essential ingredient of bread. ESTABLISH v. 1) found, create, institute, set up, start, begin, inaugurate, organize, form, constitute; decree, enact, ordain, introduce: The company was established in 1796. A new law was established to protect consumers. 2) secure, settle, fix, entrench, install or instal, seat, ensconce; lodge, locate; station: Hitler became established as dictator in 1933. Are you established in your new house? 3 prove, confirm, certify, verify, affirm, determine, authenticate, demonstrate, show, substantiate, corroborate, validate, support, back (up) : It will be difficult to establish exactly how the crime was committed.