The Collaborative International Dictionary of English v.0.48:

Cadillac \Ca*dil"lac\, n. [Prob. from Cadillac, a French town.]
   A large pear, shaped like a flattened top, used chiefly for
   cooking. --Johnson.

   2. [From Cadillac, the high-end expensive line of automobiles
      made by General Motors, often thought of as the best
      American-made automobile.] The best; -- metaphorical, from
      the automobile. Often used in the phrase "the Cadillac of
      . . . "
      [PJC]

U.S. Gazetteer Places (2000):

Cadillac, MI -- U.S. city in Michigan
   Population (2000):    10000
   Housing Units (2000): 4466
   Land area (2000):     6.821254 sq. miles (17.666967 sq. km)
   Water area (2000):    1.779726 sq. miles (4.609468 sq. km)
   Total area (2000):    8.600980 sq. miles (22.276435 sq. km)
   FIPS code:            12320
   Located within:       Michigan (MI), FIPS 26
   Location:             44.250962 N, 85.413696 W
   ZIP Codes (1990):     49601
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Cadillac, MI
    Cadillac