The Collaborative International Dictionary of English v.0.48:

Exercise \Ex"er*cise\, v. t. [imp. & p. p. Exercised; p. pr. &
   vb. n. Exercising.]
   1. To set in action; to cause to act, move, or make exertion;
      to give employment to; to put in action habitually or
      constantly; to school or train; to exert repeatedly; to
      busy.
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            Herein do I Exercise myself, to have always a
            conscience void of offence.           --Acts xxiv.
                                                  16.
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   2. To exert for the sake of training or improvement; to
      practice in order to develop; hence, also, to improve by
      practice; to discipline, and to use or to for the purpose
      of training; as, to exercise arms; to exercise one's self
      in music; to exercise troops.
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            About him exercised heroic games
            The unarmed youth.                    --Milton.
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   3. To occupy the attention and effort of; to task; to tax,
      especially in a painful or vexatious manner; harass; to
      vex; to worry or make anxious; to affect; to discipline;
      as, exercised with pain.
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            Where pain of unextinguishable fire
            Must exercise us without hope of end. --Milton.
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   4. To put in practice; to carry out in action; to perform the
      duties of; to use; to employ; to practice; as, to exercise
      authority; to exercise an office.
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            I am the Lord which exercise loving-kindness,
            judgment, and righteousness in the earth. --Jer. ix.
                                                  24.
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            The people of the land have used oppression and
            exercised robbery.                    --Ezek. xxii.
                                                  29.
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WordNet (r) 3.0 (2006):

exercising
    n 1: the activity of exerting your muscles in various ways to
         keep fit; "the doctor recommended regular exercise"; "he
         did some exercising"; "the physical exertion required by
         his work kept him fit" [syn: exercise, exercising,
         physical exercise, physical exertion, workout]