critical, essential, imperative, indispensable, integral, must-have, necessary, necessitous, needed, needful, required, requisite, vital

prerequisitecompulsory, mandatory, nonelective, obligatoryconsequential, crucial, important, major, material, meaningful, momentous, significant, substantial, weightybasic, central, fundamental, key, organicinsistent, persistent, pressing, urgent

of the essence

dispensable, inessential, needless, nonessential, unessential, unnecessary, unneeded

undesired, unwantedinconsequential, insignificant, unimportantexcess, external, extra, extraneous, superfluous, surplus