The Collaborative International Dictionary of English v.0.48:

Derby \Der"by\ (?; usually ? in Eng.; 85), n.
   1. A race for three-old horses, run annually at Epsom (near
      London), for the Derby stakes. It was instituted by the
      12th Earl of Derby, in 1780.
      [1913 Webster]

   Derby Day, the day of the annual race for the Derby stakes,
      -- Wednesday of the week before Whitsuntide.
      [1913 Webster]

   2. A stiff felt hat with a dome-shaped crown.
      [1913 Webster]

U.S. Gazetteer (1990):

Derby, CO (CDP, FIPS 20275)
  Location: 39.83945 N, 104.91808 W
  Population (1990): 6043 (2283 housing units)
  Area: 4.6 sq km (land), 0.0 sq km (water)
Derby, CT (city, FIPS 19480)
  Location: 41.32667 N, 73.08279 W
  Population (1990): 12199 (5269 housing units)
  Area: 12.9 sq km (land), 1.0 sq km (water)
  Zip code(s): 06418
Derby, IA (city, FIPS 20125)
  Location: 40.92993 N, 93.45674 W
  Population (1990): 135 (68 housing units)
  Area: 0.7 sq km (land), 0.0 sq km (water)
  Zip code(s): 50068
Derby, IN
  Zip code(s): 47525
Derby, KS (city, FIPS 17800)
  Location: 37.54930 N, 97.25887 W
  Population (1990): 14699 (5002 housing units)
  Area: 12.0 sq km (land), 0.0 sq km (water)
  Zip code(s): 67037
Derby, ME
  Zip code(s): 04463
Derby, NY
  Zip code(s): 14047
Derby, VT
  Zip code(s): 05829

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "Derby":
   Kentucky Derby, Preakness Stakes, chase, flat race, handicap,
   handicap race, harness race, horse race, hurdle race, plate race,
   purse race, quarter-horse race, stake, stake race, steeplechase,
   sweep, sweepstake, sweepstakes, trotting race



Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "derby":
   Le Mans, Olympic games, Olympics, air race, automobile race,
   bicycle race, boat race, bout, concours, contest, contest of speed,
   cross-country race, dash, dog race, drag race, encounter,
   endurance race, engagement, fight, footrace, game, games, go,
   gymkhana, heat, hurdle race, joust, lap, marathon, marathon race,
   match, match race, matching, meet, meeting, motorcycle race,
   obstacle race, potato race, race, rally, regatta, relay,
   relay race, rencontre, road race, run, sack race, speedway race,
   sprint, sprint race, stock-car race, test, three-legged race, tilt,
   torch race, tournament, tourney, track race, trial, walk,
   yacht race