As "bi-cycle" refers to a two-wheeled vehicle propelled by pedals, its antonyms would be words which represent vehicles that have either more or fewer wheels. Some antonyms that could be considered for bi-cycle are unicycle, which has just one wheel, tricycle which has three wheels, and quad bike or ATV, which is a four-wheeled vehicle. In addition, other antonyms for bi-cycle could be words that are completely unrelated to it, such as car, motorcycle, or airplane. The opposite of bi-cycle may vary depending on the context, but it usually refers to a different type of vehicle that serves a different purpose.