The Collaborative International Dictionary of English v.0.48:

gymnastics \gym*nas"tics\ (j[i^]m*n[a^]s"t[i^]ks), n.
   1. Athletic or disciplinary exercises; the art of performing
      gymnastic exercises.
      [1913 Webster]

   2. Disciplinary exercises for the intellect or character.
      [1913 Webster]

   3. [fig.] Feats demonstrating a quick mental agility; as,
      mental gymnastics, verbal gymnastics.
      [PJC] Gymnic

WordNet (r) 3.0 (2006):

gymnastics
    n 1: a sport that involves exercises intended to display
         strength and balance and agility [syn: gymnastics,
         gymnastic exercise]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "gymnastics":
   Rugby, acrobatics, agonistics, association football, athletics,
   bathing, breather, calisthenics, constitutional, daily dozen,
   drill, eurythmics, exercise, exercising, gymnastic exercises,
   isometrics, natation, palaestra, physical culture,
   physical education, physical jerks, practice, rugger,
   setting-up exercises, soccer, sports, stretch, swimming, track,
   track and field, tumbling, workout, yoga