Answer: Jiffy

The word “jiffy” has been in use since the 18th century. Although the origins of the word are unclear it is believed to have originated from criminal slang for something that was fast as lightning.

From there, it moved into popular usage to describe quick things. In the 19th century, Gilbert Newton Lewis–an American chemist–was the first to apply the term “jiffy” to technical endeavors. He used jiffy to stand in for the time it took light to travel one centimeter (approximately 33.4 picoseconds).

After Lewis’s application, the term crept into usage in other scientific pursuits. In electronics a jiffy is the time between alternating power cycles (1/60th of a second for most systems). In computing, a jiffy is one tick of the system timer (as such, a computing jiffy is not a fixed unit of time but an OS/hardware dependent unit of time). In astro and quantum physics, a jiffy is the time it takes light to travel one ferni (the width of a nucleon) and amounts to 3 × 10^-24 seconds

Although jiffy has established itself in multiple scientific communities, it was hardly constrained to use by the technically inclined. Anytime you see a Jiffy Lube oil shop, Jiffy Pop popping corn, or here people exclaim that they’ll be back in a jiffy, you’re seeing a 300 year old word alive and well in modern use.