Wiktionary:Word of the day/2026/June 3

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derailleur n (cycling)

A mechanism on a bicycle wheel used while cycling to move the bicycle chain from one sprocket (gear) to another, to change speeds. The entire gearset on a bicycle with such a mechanism. Today is World Bicycle Day, which is recognized by the United Nations to highlight the bicycle as a simple, affordable, and sustainable form of transport.

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