imperative

adjective

1 it is imperative that you find him:

vitally important, of vital importance, all-important, vital, crucial, critical, essential, of the essence, a matter of life and death, of great consequence, necessary, indispensable, exigent, pressing, urgent;

required, compulsory, mandatory, obligatory.

▷antonyms unimportant; optional.

2 the imperative note in her voice was unmistakable:

peremptory, commanding, imperious, authoritative, masterful, lordly, magisterial, autocratic, dictatorial, domineering, overbearing, assertive, firm, insistent, bossy, high-handed, overweening.

▷antonyms submissive.

imperative Oxford Dictionary of English