unicycle

noun

1. a vehicle with one wheel, especially a pedal-driven device kept upright and steered by body balance, commonly used by acrobats and other performers.

verb (used without object), u·ni·cy·cled, u·ni·cy·cling.

2. to ride a unicycle.

noun

1. a one-wheeled vehicle driven by pedals, esp one used in a circus, etcAlso called: monocycle

n.1869, American English, from Latin uni- “one” (see uni-) + -cycle, from bicycle (from Greek kyklos “circle, wheel”).