The Collaborative International Dictionary of English v.0.48:

Active \Ac"tive\, a. [F. actif, L. activus, fr. agere to act.]
   1. Having the power or quality of acting; causing change;
      communicating action or motion; acting; -- opposed to
      passive, that receives; as, certain active principles;
      the powers of the mind.
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   2. Quick in physical movement; of an agile and vigorous body;
      nimble; as, an active child or animal.
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            Active and nervous was his gait.      --Wordsworth.
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   3. In action; actually proceeding; working; in force; --
      opposed to quiescent, dormant, or extinct; as,
      active laws; active hostilities; an active volcano.
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   4. Given to action; constantly engaged in action; energetic;
      diligent; busy; -- opposed to dull, sluggish,
      indolent, or inert; as, an active man of business;
      active mind; active zeal.
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   5. Requiring or implying action or exertion; -- opposed to
      sedentary or to tranquil; as, active employment or
      service; active scenes.
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   6. Given to action rather than contemplation; practical;
      operative; -- opposed to speculative or theoretical;
      as, an active rather than a speculative statesman.
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   7. Brisk; lively; as, an active demand for corn.
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   8. Implying or producing rapid action; as, an active disease;
      an active remedy.
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   9. (Gram.)
      (a) Applied to a form of the verb; -- opposed to
          passive. See Active voice, under Voice.
      (b) Applied to verbs which assert that the subject acts
          upon or affects something else; transitive.
      (c) Applied to all verbs that express action as distinct
          from mere existence or state.
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   Active capital, Active wealth, money, or property that
      may readily be converted into money.
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   Syn: Agile; alert; brisk; vigorous; nimble; lively; quick;
        sprightly; prompt; energetic.
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WordNet (r) 3.0 (2006):

active
    adj 1: tending to become more severe or wider in scope; "active
           tuberculosis" [ant: inactive]
    2: engaged in or ready for military or naval operations; "on
       active duty"; "the platoon is combat-ready"; "review the
       fighting forces" [syn: active, combat-ready,
       fighting(a)]
    3: disposed to take action or effectuate change; "a director who
       takes an active interest in corporate operations"; "an active
       antagonism"; "he was active in drawing attention to their
       grievances" [ant: inactive, passive]
    4: taking part in an activity; "an active member of the club";
       "he was politically active"; "the participating
       organizations" [syn: active, participating]
    5: characterized by energetic activity; "an active toddler";
       "active as a gazelle"; "an active man is a man of action"
       [ant: inactive]
    6: exerting influence or producing a change or effect; "an
       active ingredient" [ant: inactive]
    7: full of activity or engaged in continuous activity; "an
       active seaport"; "an active bond market"; "an active account"
       [ant: inactive]
    8: in operation; "keep hope alive"; "the tradition was still
       alive"; "an active tradition" [syn: active, alive(p)]
    9: (of the sun) characterized by an increased occurrence of
       sunspots and flares and radio emissions [ant: quiet]
    10: expressing that the subject of the sentence has the semantic
        function of actor: "Hemingway favors active constructions"
        [ant: passive]
    11: (used of verbs (e.g. `to run') and participial adjectives
        (e.g. `running' in `running water')) expressing action
        rather than a state of being [syn: active, dynamic]
        [ant: stative]
    12: (of e.g. volcanos) capable of erupting [ant: extinct]
    13: (of e.g. volcanos) erupting or liable to erupt; "active
        volcanos" [ant: dormant, inactive]
    14: engaged in full-time work; "active duty"; "though past
        retirement age he is still active in his profession" [ant:
        inactive]
    n 1: chemical agent capable of activity [syn: active agent,
         active]
    2: the voice used to indicate that the grammatical subject of
       the verb is performing the action or causing the happening
       denoted by the verb; "`The boy threw the ball' uses the
       active voice" [syn: active voice, active] [ant:
       passive, passive voice]
    3: a person who is a participating member of an organization;
       "the club issues a list of members, both the actives and the
       retirees"