[1] : The Collaborative International Dictionary of English v.0.48

imperative \imper"ative\, a. l. imperativus, fr. imperare to
   command; pref. im- in + parare to make ready, prepare: cf. f.
   imp'eratif. see perade, and cf. empire.
   1. expressive of command; containing positive command;
      authoritatively or absolutely directive; commanding;
      authoritative; as, imperative orders.
      1913 webster

            the suit of kings are imperative.     --bp. hall.
      1913 webster

   2. not to be avoided or evaded; obligatory; binding;
      compulsory; as, an imperative duty or order.
      1913 webster

   3. gram. expressive of command, entreaty, advice, or
      exhortation; as, the imperative mood.
      1913 webster
see also:
perade empire 

[2] : The Collaborative International Dictionary of English v.0.48

imperative \imper"ative\, n. gram.
   the imperative mood; also, a verb in the imperative mood.
   1913 webster

[3] : WordNet (r) 2.0

imperative
     adj 1: requiring attention or action; "as nuclear weapons
            proliferate, preventing war becomes imperative";
            "requests that grew more and more imperative" ant: beseeching
     2: relating to verbs in the imperative mood
     n 1: a mood that expresses an intention to influence the
          listener's behavior syn: imperative mood, jussive
          mood
     2: some duty that is essential and urgent
see also:
beseeching imperative mood jussive mood 

[4] : Moby Thesaurus II by Grady Ward, 1.0

256 moby thesaurus words for "imperative":
   absolute, absolutist, absolutistic, acid, acute, allegiance,
   arbitrary, aristocratic, arrogant, ascendant, assigned task,
   authoritarian, authoritative, authorized, autocratic, basic,
   behest, bidding, binding, biting, bossy, bounden duty, burden,
   burning, business, call of duty, canon, case of need, charge,
   choiceless, claimed, clamant, clamorous, clothed with authority,
   coactive, code, command, commanding, commandment, commitment,
   compelling, competent, compulsatory, compulsive, compulsory,
   conclusive, conditional, consequential, considerable, constraining,
   controlling, convention, corrosive, critical, crucial, crying,
   cutting, de rigueur, decisive, decretal, decretive, decretory,
   dedication, deference, demanded, despotic, devoir, devotion,
   dictate, dictated, dictating, dictation, dictatorial, dictum,
   dire necessity, direct order, directive, dogmatic, dominant,
   domineering, driving, duly constituted,
   duties and responsibilities, duty, effective, eminent, empowered,
   entailed, essential, ethics, ex officio, exigence, exigency,
   exigent, fealty, feudal, final, forceful, forcible, form, formula,
   fundamental, general principle, golden rule, governing, great,
   grinding, guideline, guiding principle, gutsy, hard-and-fast,
   harsh, hegemonic, hegemonistic, hest, high-handed, high-pressure,
   high-priority, homage, immediacy, imperativeness, imperial,
   imperious, important, importunate, imposed, impressive, incisive,
   indicative, indispensable, inevitable, influential, insistent,
   instant, instructive, involuntary, irresistible, irrevocable,
   jussive, law, leading, line of duty, lordly, loyalty, magisterial,
   magistral, mandated, mandating, mandatory, masterful,
   matter of necessity, maxim, mighty, mission, mitzvah, mode,
   momentous, monocratic, mood, moral, mordant, must, necessary,
   necessitous, nervous, norm, obligating, obligation, obligative,
   obligatory, official, onus, oppressive, optative, order, ordering,
   ordinance, ought, overbearing, overruling, penetrating, peremptory,
   permissive, piercing, pivotal, place, pleasure, poignant, potent,
   potential, powerful, preceptive, predicament, preeminent,
   prerequisite, prescript, prescriptive, pressing, pressingness,
   pressure, prestigious, principium, principle, prominent, puissant,
   punchy, ranking, regulation, repressive, required, requisite,
   respect, restraining, rubric, rule, ruling, say-so,
   self-imposed duty, senior, sensational, settled principle, severe,
   sinewed, sinewy, slashing, special order, standard, stern, strict,
   striking, strong, subjunctive, substantial, superior, suppressive,
   supreme, telling, tenet, totalitarian, trenchant, tyrannical,
   tyrannous, ultimate, urgency, urgent, urgent need, vigorous, vital,
   weighty, will, without appeal, without choice, word,
   word of command, working principle, working rule

Imperative >> I Words
Imperative, definition of term: Imperative
imperative_pag1.html

Imperative Mood >> I Words
Imperative Mood, definition of term: Imperative Mood
imperative+mood_pag1.html