Expressing a command or plea; peremptory: requests that grew more and more imperative. Having the power or authority to command or control. Grammar Of, relating to, or constituting the mood that expresses a command or request. Impossible to deter or evade; pressing: imperative needs. See Synonyms at urgent. A command; an order. An obligation; a duty: social imperatives. A rule, principle, or instinct that compels a certain behavior: a people driven to aggression by territorial imperatives. Grammar The imperative mood. Grammar A verb form of the imperative mood.