The Collaborative International Dictionary of English v.0.48:

Gymnast \Gym"nast\ (j[i^]m"n[.a]st), n. [Gr. gymnasth`s a
   trainer of athletes: cf. F. gymnaste. See Gymnasium.]
   One who teaches or practices gymnastic exercises; the manager
   of a gymnasium; an athlete. Gymnastic

WordNet (r) 3.0 (2006):

gymnast
    n 1: an athlete who is skilled in gymnastics