WordNet (r) 3.0 (2006):

broncobuster
    n 1: a person who breaks horses [syn: buster, bronco buster,
         broncobuster]

Moby Thesaurus II by Grady Ward, 1.0:

53 Moby Thesaurus words for "broncobuster":
   breaker, breeder, buckaroo, caballero, cattleman, cavalier,
   cavalryman, chevalier, circus rider, cow keeper, cowboy, cowgirl,
   cowman, cowpuncher, dairy farmer, dairyman, equerry, equestrian,
   equestrienne, farrier, gaucho, grazier, groom, horse soldier,
   horseback rider, horsebacker, horseman, horseshoer, horsewoman,
   hostler, jockey, knight, mounted policeman, postboy, postilion,
   puncher, rancher, ranchero, ranchman, rider, roughrider, sheepman,
   stableboy, stableman, steeplechaser, stock raiser, stockbreeder,
   stockkeeper, stockman, tamer, trainer, trick rider, vaquero