1a gear in a motor vehicle providing a gear ratio higher than that of direct drive (the usual top gear), so that the engine speed can be reduced at high road speeds to lessen fuel consumption or to allow further acceleration.
a mechanism which permits the exceeding of some normal operating level in a piece of equipment, especially the amplifier of an electric guitar.
2 [mass noun] a state of great or excessive activity:the city’s worried public relations group went into overdrive
[with object] (usually as adjective overdriven)
1drive or work to exhaustion:an overdriven mother of ten children
2give (an electric guitar) a distorted sound:pounding drums and overdriven electric guitars
overdrive in other Oxford dictionaries
Definition of overdrive in the US English dictionary