Definition of yocto- in English:

yocto-

Pronunciation /ˈyäːktō-/ /ˈjɑːktoʊ-/

  • (used in units of measurement) denoting a factor of 10⁻²⁴

    • ‘yoctojoule’

Origin

Adapted from octo-, on the pattern of combining forms such as peta- and exa-.