Source : Webster's Revised Unabridged Dictionary (1913)

Equestrian \E*ques"tri*an\, a. [L. equester, from eques
   horseman, fr. equus horse: cf. F. ['e]questre. See {Equine}.]
   1. Of or pertaining to horses or horsemen, or to
      horsemanship; as, equestrian feats, or games.

   2. Being or riding on horseback; mounted; as, an equestrian
      statue.

            An equestrian lady appeared upon the plains.
                                                  --Spectator.

   3. Belonging to, or composed of, the ancient Roman equities
      or knights; as, the equestrian order. --Burke.

Equestrian \E*ques"tri*an\, n.
   One who rides on horseback; a horseman; a rider.

Source : WordNet®

equestrian
     adj 1: of or relating to or composed of knights
     2: of or relating to or featuring horseback riding
     n : a man skilled in equitation [syn: {horseman}, {horseback
         rider}]