Im*per"a*tive (?), a. [L. imperativus, fr. imperare to command; pref. im- in + parare to make ready, prepare: cf. F. impératif. See Perade, and cf. Empire.] 1. Expressive of command; containing positive command; authoritatively or absolutely directive; commanding; authoritative; as, imperative orders.

The suit of kings are imperative.

2. Not to be avoided or evaded; obligatory; binding; compulsory; as, an imperative duty or order.

3. (Gram.) Expressive of commund, entreaty, advice, or exhortation; as, the imperative mood.

Im*per"a*tive, n. (Gram.) The imperative mood; also, a verb in the imperative mood.

• (Grammar): The verbal mood expressing an order. In English, the imperative is the same as the second person ("you") form of the verb
        The verbs in sentences like "Get it." and "Say what you like" are in the imperative.
  
• An essential action, a must: something which is imperative.
       Visiting Berlin is an imperative.
  
• essential.
       It is imperative that you come here right now.
  
• (comptheory) Having a semantics that incorporates mutable variables.