The Collaborative International Dictionary of English v.0.48:

Equerry \Eq"uer*ry\ (?; 277), n.; pl. Equerries. [F. ['e]curie
   stable, for older escurie, escuirie (confused somewhat with
   F. ['e]cuyer, OF. escuyer, squire), LL. scuria, OHG. skiura,
   sc?ra, barn, shed, G. scheuer, from a root meaning to cover,
   protect, and akin to L. scutum shield. See Esquire, and cf.
   Ecurie, Querry.]
   1. A large stable or lodge for horses. --Johnson.
      [1913 Webster]

   2. An officer of princes or nobles, charged with the care of
      their horses.
      [1913 Webster]

   Note: In England equerries are officers of the royal
         household in the department of the Master of the Horse.
         [1913 Webster]

WordNet (r) 3.0 (2006):

equerry
    n 1: an official charged with the care of the horses of princes
         or nobles
    2: a personal attendant of the British royal family

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "equerry":
   boy, breaker, breeder, broncobuster, buckaroo, butler, cattleman,
   chauffeur, coachman, cow keeper, cowman, dairy farmer, dairyman,
   driver, farrier, gardener, gentleman, gillie, grazier, groom,
   horseshoer, hostler, houseboy, houseman, lord-in-waiting, man,
   manservant, rancher, ranchero, ranchman, sheepman, stableboy,
   stableman, stock raiser, stockbreeder, stockkeeper, stockman,
   tamer, trainer, valet, valet de chambre