The Collaborative International Dictionary of English v.0.48:

Vigor \Vig"or\, n. [OE. vigour, vigor, OF. vigor, vigur, vigour,
   F. vigueur, fr. L. vigor, fr. vigere to be lively or strong.
   See Vegetable, Vigil.]
   1. Active strength or force of body or mind; capacity for
      exertion, physically, intellectually, or morally; force;
      energy.
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            The vigor of this arm was never vain. --Dryden.
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   2. Strength or force in animal or vegetable nature or action;
      as, a plant grows with vigor.
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   3. Strength; efficacy; potency.
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            But in the fruithful earth . . .
            His beams, unactive else, their vigor find.
                                                  --Milton.
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   Note: Vigor and its derivatives commonly imply active
         strength, or the power of action and exertion, in
         distinction from passive strength, or strength to
         endure.
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The Collaborative International Dictionary of English v.0.48:

Vigor \Vig"or\, v. t.
   To invigorate. [Obs.] --Feltham.
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WordNet (r) 3.0 (2006):

vigor
    n 1: forceful exertion; "he plays tennis with great energy";
         "he's full of zip" [syn: energy, vigor, vigour,
         zip]
    2: active strength of body or mind [syn: vigor, vigour,
       dynamism, heartiness]
    3: an imaginative lively style (especially style of writing);
       "his writing conveys great energy"; "a remarkable muscularity
       of style" [syn: energy, muscularity, vigor, vigour,
       vim]