a one wheeled device, somewhat difficult to balance
a single-wheeled vehicle traditionally used during circus performances
a vehicle with one wheel that is moved by pedals
cycle of the one-wheel, with cyclist on the wheel.
A circus apparatus, a one-wheel bicycle with a small seat or without seat.
A one wheeled bike with no handle bars.
A unicycle is a one-wheeled human powered vehicle. Unicycles are similar to, but less complex than, bicycles.
The term unicycle is often used in robotics and control theory to mean a generalised cart or car moving in a two-dimensional world; these are also often called "unicycle-like" or "unicycle-type" vehicles. This usage is distinct from the literal sense of "one wheeled robot bicycle".