from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A device for shifting gears on a bicycle by moving the chain between sprocket wheels of different sizes.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The mechanism on a bicycle used to move the chain from one sprocket (gear) to another.
- n. The entire gearset on a bicycle with such a mechanism.
French dérailleur, from dérailler, to derail; see derail.(American Heritage® Dictionary of the English Language, Fourth Edition)
From French dérailleur. (Wiktionary)