imperative

nouns

a mood that expresses an intention to influence the listener's behavior
some duty that is essential and urgent
is a type of (narrower)
the social force that binds you to the courses of action demanded by that force
"we must instill a sense of duty in our children"; "every right implies a responsibility; every opportunity, an obligation; every possession, a duty"- John D.Rockefeller Jr

adjectives

requiring attention or action
"as nuclear weapons proliferate, preventing war becomes imperative"; "requests that grew more and more imperative"
is derived from
antonym
is similar to
containing a solemn charge or command
is similar to
demanding attention
"clamant needs"; "a crying need"; "regarded literary questions as exigent and momentous"- H.L.Mencken; "insistent hunger"; "an instant need"
is similar to
not allowing contradiction or refusal
"spoke in peremptory tones"; "peremptory commands"
is similar to
showing extreme urgency or intensity especially because of great need or desire
"felt a desperate urge to confess"; "a desperate need for recognition"
is similar to
compelling immediate action
"too pressing to permit of longer delay"; "the urgent words `Hurry! Hurry!'"; "bridges in urgent need of repair"
is similar to
being sharply insistent on being heard
"strident demands"; "shrill criticism"
see also
aggressively self-assured
"an energetic assertive boy who was always ready to argue"; "pointing directly at a listener is an assertive act"
relating to verbs in the imperative mood
pertains to
domain category
the branch of linguistics that deals with syntax and morphology (and sometimes also deals with semantics)