noun at·to·sec·ond \ˈa-(ˌ)tō-ˌse-kənd, -kənt\

Definition of attosecond

  1. :  one quintillionth (10−18) of a second An attosecond is to a second what a second is to the age of the universe. — IEEE Spectrum

Origin and Etymology of attosecond

atto- + 3second

First Known Use: 1962

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