absolutely necessary or required; unavoidable

It is imperative that we leave.

of the nature of or expressing a command; commanding.

Grammar . noting or pertaining to the mood of the verb used in commands, requests, etc., as in Listen! Go! Compare indicative ( def. 2 ) , subjunctive ( def. 1 ) .

a command.

something that demands attention or action; an unavoidable obligation or requirement; necessity

It is an imperative that we help defend friendly nations.

Grammar .

the imperative mood.

a verb in this mood.

an obligatory statement, principle, or the like.

adjective

inessential , optional , secondary , unnecessary , voluntary , discretionary , free , unrestrained

adjective

acute , burning , clamant , clamorous , compulsory , critical , crucial , crying , essential , exigent , immediate , important , importunate , indispensable , inescapable , insistent , instant , no turning back , obligatory , pressing , urgent , vital , aggressive , autocratic , bidding , bossy , commanding , dictatorial , dominant , domineering , harsh , high-handed , imperial , imperious , ordering , overbearing , peremptory , powerful , stern , dire , emergent , mandatory , necessary , requisite , absolute , binding , cogent , command , compulsatory , demanding , de rigueur , duty , order , preemptory , prerequisite , required , rule

noun

burden , charge , commitment , must , need , obligation , responsibility