freewheel

[ free-hweel, -weel ]
/ ˈfriˈʰwil, -ˈwil /

noun

a device in the transmission of a motor vehicle that automatically disengages the drive shaft whenever it begins to turn more rapidly than the engine.
a form of rear bicycle wheel that has a device freeing it from the driving mechanism, as when the pedals are stopped in coasting.

verb (used without object)

(of a vehicle or its operator) to coast with the wheels disengaged from the driving mechanism.
to move or function freely, independently, unconcernedly, or the like (often followed by about, through, around, etc.): The two friends freewheeled around the country after graduation.

Origin of freewheel

First recorded in 1895–1900; free + wheel

British Dictionary definitions for freewheel

freewheel
/ (ˌfriːˈwiːl) /

noun

a ratchet device in the rear hub of a bicycle wheel that permits the wheel to rotate freely while the pedals are stationary
a device in the transmission of some vehicles that automatically disengages the drive shaft when it rotates more rapidly than the engine shaft, so that the drive shaft can turn freely

verb

(intr) to coast in a vehicle or on a bicycle using the freewheel