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noun de·rail·leur \di-ˈrā-lər\

Simple Definition of derailleur

  • : a part on a bicycle that is used to change gears by moving the chain from one gear to another one

Source: Merriam-Webster's Learner's Dictionary

Full Definition of derailleur

  1. :  a mechanism for shifting gears on a bicycle that operates by moving the chain from one set of exposed gears to another

Origin and Etymology of derailleur

French dérailleur, from dérailler

First Known Use: 1930

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