The term 'derailleur' describes a key component of a bicycle, responsible for shifting gears. While this word is commonly used among cycling enthusiasts, there are several synonyms that can be used to describe the same component. Some of the most common synonyms for derailleur include 'gear changer', 'mech', 'gear shift', 'derailer', 'gear shifter', and 'gear derailleur'. These words can be useful when trying to convey information about a bike to someone who isn't familiar with cycling jargon. In short, there are plenty of interchangeable terms for derailleur, but they all describe the same thing - a mechanism that allows cyclists to change gears while riding.