overdrive

1. A gear, on an automobile, higher than the traditional top gear, mainly to allow better fuel economy at highway speeds. In the 21st century, such gears are no longer viewed as "extra" and thus rarely called by this name. (countable, dated, uncountable) · Near-synonym: top gear· In the 1970s, many transmission designs were revised to add an overdrive gear.
2. A state of heightened activity. (figuratively, uncountable) · overdrive pacing· The campaign has been in overdrive since the recent announcement.
3. Freewheeling (driving a vehicle with the transmission in neutral) on downhill stretches to achieve higher fuel economy and/or speed than otherwise. In colloquial registers, ethnically bigoted variants have been common, such as Jewish overdrive (alluding to the stereotype of miserly Jews) or Mexican overdrive or Polish overdrive (alluding to stereotypes of foolishness and poverty). (countable, slang, uncountable)
4. A gear ratio higher than 1:1: one in which a single revolution of the driving element corresponds to more than one revolution of the driven element. (countable, uncountable)

Plural overdrives