Noun

• S: (n) imperative mood, imperative, jussive mood, imperative form (a mood that expresses an intention to influence the listener's behavior)
• S: (n) imperative (some duty that is essential and urgent)

Adjective

• S: (adj) imperative (requiring attention or action) "as nuclear weapons proliferate, preventing war becomes imperative"; "requests that grew more and more imperative"
• S: (adj) imperative (relating to verbs in the imperative mood)