imperative

adj. necessary, obligatory; commanding; of the imperative mood, of the form used when making an order or request (Grammar); of a verb in the imperative mood (Grammar)

n. necessity, obligation; command, order; imperative mood, form used when making an order or request (Grammar); verb in the imperative mood (Grammar)

Imperative can mean:Imperative programming, in computer science, a programming paradigmImperative mood, a grammatical mood expressing commands, direct requests, and prohibitionsMoral imperative, a philosophical concept relating to obligation.
See more at Wikipedia.org...

Noun
1. a mood that expresses an intention to influence the listener's behavior
(synonym) imperative mood, jussive mood
(hypernym) mood, mode, modality
2. some duty that is essential and urgent
(hypernym) duty, responsibility, obligation
Adjective
1. requiring attention or action; "as nuclear weapons proliferate, preventing war becomes imperative"; "requests that grew more and more imperative"
(antonym) beseeching
(similar) adjuratory
(see-also) assertive
2. relating to verbs in the imperative mood
(pertainym) imperative mood, jussive mood
(classification) grammar

n. imperative, imperative mode, form used when making an order or request, verb in the imperative mood (Grammar)

adj. imperative, necessary