A mechanism on a bicycle or motorcycle that shifts the chain between different gears.
From French 'dérailleur' (literally 'derailer'). Named because it works by momentarily lifting the chain off its sprocket, roughly 'derailing' it to shift gears.
It's hilarious that the fancy mechanism making your bike shift gears smoothly is literally called a 'derailer'—because it temporarily derails the chain to make gear changes work! The name is kind of a joke.
Complete word intelligence in one call. Free tier — 50 lookups/day.