A riding machine with a single wheel, a seat on a post above it, and pedals fixed straight onto the wheel — no handlebars, no chain, no second wheel to hold you up. Staying on one takes real practice, because you must balance forwards and backwards as well as side to side, and you steer by twisting your body. Most people meet unicycles at a circus, at a street performance, or in videos of people doing tricks; a few use them to get around, and there are mountain unicycles for rough ground. Note that the pedals turn with the wheel, so you cannot coast — stop pedalling and you fall. As a verb, to unicycle means to ride one, though people usually say 'ride a unicycle' instead. The word carries a small flavour of showing off a difficult, useless-looking skill, which is why 'he can juggle and unicycle' sounds funny rather than impressive in an ordinary conversation.