derailleur

[ dih-rey-ler ]
/ dɪˈreɪ lər /

noun

a gear-shifting mechanism on a bicycle that shifts the drive chain from one sprocket wheel to another.

Origin of derailleur

1945–50; < French dérailleur literally, a device causing disengagement or derailing, equivalent to déraill(er) to derail + -eur -eur
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for derailleur

derailleur

/ (dəˈreɪljə) /

noun

a mechanism for changing gear on bicycles, consisting of a device that lifts the driving chain from one sprocket wheel to another of different size

Word Origin for derailleur

French dérailleur derailer
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012