Unicycle is a modern coinage from Latin uni- ('one', from unus) + cycle, from Ancient Greek kyklos ('circle, wheel'), on the model of bicycle and tricycle. Important recorded forms include unus (Latin), κύκλος (Ancient Greek), and *kʷekʷlos (Proto-Indo-European). Morphologically, the word preserves a built structure whose named elements carry the historical sense into English. The modern sense continues the older lexical line without requiring a separate origin. In current use it covers a single-wheeled pedal-driven vehicle. The wider family includes derived forms such as unicyclist and unicycling and related words such as bicycle, tricycle, and cycle.