The Collaborative International Dictionary of English v.0.48:

Energetic \En`er*get"ic\, Energetical \En`er*get"ic*al\, a. [Gr.
   ?, fr. ? to work, be active, fr. ? active. See Energy.]
   1. Having energy or energies; possessing a capacity for
      vigorous action or for exerting force; active. "A Being
      eternally energetic." --Grew.
      [1913 Webster]

   2. Exhibiting energy; operating with force, vigor, and
      effect; forcible; powerful; efficacious; as, energetic
      measures; energetic laws.

   Syn: Forcible; powerful; efficacious; potent; vigorous;
        effective; strenuous. -- En`er*get"ic*al*ly, adv. --
        En`er*get"ic*al*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

energetic
    adj 1: possessing or exerting or displaying energy; "an
           energetic fund raiser for the college"; "an energetic
           group of hikers"; "it caused an energetic chemical
           reaction" [ant: lethargic, unenrgetic]
    2: working hard to promote an enterprise [syn: energetic,
       gumptious, industrious, up-and-coming]