The Collaborative International Dictionary of English v.0.48:

Ferris wheel \Fer"ris wheel\
   An amusement device consisting of a giant power-driven
   vertically oriented steel wheel, revolvable on its horizontal
   stationary axle, and carrying a number of balanced passenger
   cars or open seats around its rim; the seats are suspended so
   as to remain horizontal as the wheel rotates, and, depending
   on the size of the wheel, the passengers when they reach the
   top may have a grand vista of the surrounding area; -- so
   called after G. W. G. Ferris, American engineer, who erected
   the first of its kind for the World's Columbian Exposition in
   Chicago in 1893.

   Note: Ferris wheels are often found at traveling fairs and at
         permanent amusement parks. The Reisenrad in Vienna is
         one of the world's largest and most famous Ferris
         wheels.
         [Webster 1913 Suppl. +PJC]

WordNet (r) 3.0 (2006):

Ferris wheel
    n 1: a vertical rotating mechanism consisting of a large wheel
         with suspended seats that remain upright as the wheel
         rotates; provides a ride at an amusement park