1. Expressing a command or plea; peremptory: requests that grew more and more imperative.
2. Having the power or authority to command or control.
3. Grammar. Of, relating to, or constituting the mood that expresses a command or request.
4. Impossible to deter or evade; pressing: imperative needs. See synonyms at urgent.

1. 1. A command; an order.
   2. An obligation; a duty: social imperatives.
2. A rule, principle, or instinct that compels a certain behavior: a people driven to aggression by territorial imperatives.
3. Grammar.
   1. The imperative mood.
   2. A verb form of the imperative mood.

[Middle English imperatif, relating to the imperative mood, from Old French, from Late Latin imperātīvus, from Latin imperātus, past participle of imperāre, to command. See emperor.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.