derailleur
UK: dɪˈreɪlə | US: dɪˈreɪlər
n. a mechanism for shifting gears on a bicycle by moving the chain from one sprocket to another.
Derived from French dérailleur (literally "derailer"), the word reflects its function of moving the bicycle chain off one sprocket track and onto another. The term emerged in the early 20th century with the development of multi-speed bicycles, combining the idea of displacement (dé) and guided movement (rail) with an instrumental suffix (-eur).
The cyclist adjusted the derailleur to switch to a lower gear for the steep climb.
Modern derailleurs allow for smooth and precise gear changes.
A misaligned derailleur can cause the chain to slip or drop.
He upgraded his bike with a high-performance derailleur for the race.
Cleaning and lubricating the derailleur regularly ensures optimal performance.