The Collaborative International Dictionary of English v.0.48:

Imperative \Im*per"a*tive\, n. (Gram.)
   The imperative mood; also, a verb in the imperative mood.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Imperative \Im*per"a*tive\, a. [L. imperativus, fr. imperare to
   command; pref. im- in + parare to make ready, prepare: cf. F.
   imp['e]ratif. 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]

WordNet (r) 3.0 (2006):

imperative
    adj 1: requiring attention or action; "as nuclear weapons
           proliferate, preventing war becomes imperative";
           "requests that grew more and more imperative" [ant:
           beseeching, imploring, pleading]
    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, imperative,
         jussive mood, imperative form]
    2: some duty that is essential and urgent

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



The Free On-line Dictionary of Computing (30 December 2018):

imperative language
imperative
imperative programming

    Any programming language that specifies explicit
   manipulation of the state of the computer system, not to be
   confused with a procedural language, which specifies an
   explicit sequence of steps to perform.

   An example of an imperative (but non-procedural) language is a
   data manipulation language for a relational database
   management system.  This specifies changes to the database
   but does not necessarily require anyone to specify a sequence
   of steps.

   Both contrast with declarative languages, which specify
   neither explicit state manipulation nor a sequence of steps.

   (2007-10-02)