The Collaborative International Dictionary of English v.0.48:

Vivacious \Vi*va"cious\ (?; 277), a. [L. v['i]vax, -acis, fr.
   vivere to live. See Vivid.]
   1. Having vigorous powers of life; tenacious of life;
      long-lived. [Obs.]
      [1913 Webster]

            Hitherto the English bishops have been vivacious
            almost to wonder. . . . But five died for the first
            twenty years of her [Queen Elizabeth's] reign.
                                                  --Fuller.
      [1913 Webster]

            The faith of Christianity is far more vivacious than
            any mere ravishment of the imagination can ever be.
                                                  --I. Taylor.
      [1913 Webster]

   2. Sprightly in temper or conduct; lively; merry; as, a
      vivacious poet. "Vivacious nonsense." --V. Knox.
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   3. (Bot.) Living through the winter, or from year to year;
      perennial. [R.]
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   Syn: Sprightly; active; animated; sportive; gay; merry;
        jocund; light-hearted.
        [1913 Webster] -- Vi*va"cious*ly, adv. --
        Vi*va"cious*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

vivacious
    adj 1: vigorous and animated; "a vibrant group that challenged
           the system"; "a charming and vivacious hostess"; "a
           vivacious folk dance" [syn: vibrant, vivacious]