Source : Webster's Revised Unabridged Dictionary (1913)

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.

   2. Quick in physical movement; of an agile and vigorous body;
      nimble; as, an active child or animal.

            Active and nervous was his gait.      --Wordsworth.

   3. In action; actually proceeding; working; in force; --
      opposed to {quiescent}, {dormant}, or {extinct}; as,
      active laws; active hostilities; an active volcano.

   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.

   5. Requiring or implying action or exertion; -- opposed to
      {sedentary} or to {tranquil}; as, active employment or
      service; active scenes.

   6. Given to action rather than contemplation; practical;
      operative; -- opposed to {speculative} or {theoretical};
      as, an active rather than a speculative statesman.

   7. Brisk; lively; as, an active demand for corn.

   8. Implying or producing rapid action; as, an active disease;
      an active remedy.

   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.

   {Active capital}, {Active wealth}, money, or property that
      may readily be converted into money.

   Syn: Agile; alert; brisk; vigorous; nimble; lively; quick;
        sprightly; prompt; energetic.

Source : WordNet®

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: {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: {passive}]
     4: taking part in an activity; "an active member of the club";
        "he was politically active"; "the participating
        organizations" [syn: {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 an 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: {alive(p)}]
     9: of the sun; characterized by a high level activity in
        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: expressing action rather than a state of being; used of
         verbs (e.g. `to run') and participial adjectives (e.g.
         `running' in `running water') [syn: {dynamic}] [ant: {stative}]
     12: (of e.g. volcanos) erupting or liable to erupt; "active
         volcanos" [ant: {dormant}, {extinct}]
     13: producing activity or change [ant: {counteractive}]
     14: engaged in full-time work; "active duty"; "though past
         retirement age he is still active in his profession"
         [ant: {inactive}]
     15: being in physical motion; "active fish in the aquarium"
     16: characterized by energetic bodily activity; "tennis is an
         active sport"; "a very physical dance performance" [syn:
         {physical}]

active
     n 1: chemical agent capable of activity [syn: {active agent}]
     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}] [ant: {passive voice}]
     3: a person devoted to the active life [ant: {contemplative}]