Source : Webster's Revised Unabridged Dictionary (1913)

Vigor \Vig"or\, v. t.
   To invigorate. [Obs.] --Feltham.

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.

            The vigor of this arm was never vain. --Dryden.

   2. Strength or force in animal or force in animal or
      vegetable nature or action; as, a plant grows with vigor.

   3. Strength; efficacy; potency.

            But in the fruithful earth . . . His beams, unactive
            else, their vigor find.               --Milton.

   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.

Source : WordNet®

vigor
     n 1: an exertion of force; "he plays tennis with great energy"
          [syn: {energy}, {vigour}]
     2: active strength of body or mind [syn: {vigour}]
     3: an imaginative lively style (especially style of writing);
        "his writing conveys great energy" [syn: {energy}, {vigour},
         {vim}]