yoctosecond


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yoc·to·sec·ond

 (yŏk′tə-sĕk′ənd)
n. Abbr. ys or ysec
One septillionth (10-24) of a second.

yoctosecond

(ˈjɒktəʊˌsɛkənd)
n
a unit of time equalling 10–24 seconds