n.
安全脚踏车

[ noun ]
bicycle that has two wheels of equal size; pedals are connected to the rear wheel by a multiplying gear
<noun.artifact>

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]