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.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
yoctosecond
(ˈjɒktəʊˌsɛkənd)n
a unit of time equalling 10–24 seconds
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014