The Oxford Thesaurus An A-Z Dictionary of Synonyms - imperativeadj.

1) mandatory, compulsory, necessary, required, requisite, demanded, obligatory, indispensable, essential, crucial, vital, urgent, pressing, exigent: It is imperative that we catch the 5.04 to London. 2) imperious, commanding, authoritarian, overbearing, peremptory, autocratic, domineering, magisterial, lordly, arbitrary, dictatorial, dogmatic, tyrannical, despotic, Colloq bossy: We were all shaken into obedience by her imperative tone.