zeptosecond
An SI unit of time equal to 10⁻²¹ seconds. Used in physics and ultrafast science.
A zeptosecond is an extremely short unit of time, 10 to the power of minus 21 seconds.
From the SI prefix 'zepto-' (10⁻²¹) combined with 秒 (second). The prefix 'zepto-' derives from Latin 'septem' (seven), as 10⁻²¹ = (10⁻³)⁷.