The Collaborative International Dictionary of English v.0.48:

Safety bicycle \Safety bicycle\
   A bicycle with equal or nearly equal wheels, usually about 28
   inches diameter, driven by pedals connected to the rear
   (driving) wheel by a multiplying gear. Since the 1930's this
   has been the most common type of bicycle, now simply called
   bicycle. The older high-wheelers are often referred to as
   bone-rattlers.
   [Webster 1913 Suppl. +PJC]

The Collaborative International Dictionary of English v.0.48:

Bicycle \Bi"cy*cle\, n. [Pref. bi- + cycle.]
   A light vehicle having two wheels one behind the other. It
   has a saddle seat and is propelled by the rider's feet acting
   on cranks or levers.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bicycle
    n 1: a wheeled vehicle that has two wheels and is moved by foot
         pedals [syn: bicycle, bike, wheel, cycle]
    v 1: ride a bicycle [syn: bicycle, cycle, bike, pedal,
         wheel]