necessary

Synonyms: all-important basic binding bottom-line cardinal chief compelling compulsory crucial decisive de rigueur elementary exigent expedient fundamental imperative incumbent on indispensable mandatory momentous name of game needed needful obligatory paramount prerequisite pressing prime principal quintessential required requisite significant specified unavoidable urgent vital wanted

Antonyms: inessential unimportant unnecessary useless

Synonyms: assured certain fated imminent ineluctable ineludible inerrant inescapable inevasible inexorable infallible returnless unavoidable undeniable unescapable

Antonyms: contingent needless optional voluntary