Synonyms for Imperative (same or very similar meaning)
WordNet sense 1 (a mood that expresses an intention to influence the listener's behavior):
imperative mood, imperative form, jussive moodWordNet sense 2 (compelling immediate action):
pressing, urgentWordNet sense 3 (not allowing contradiction or refusal):
peremptoryWordNet sense 4 (demanding attention):
crying, exigent, insistent, instantFrom the ODE community, based on WordNetadd/edit