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.