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femto-

American  

  1. a combining form used in the names of units of measurement which are 10− 15 (one quadrillionth) smaller than the unit denoted by the base word.

femto- British  

prefix

  1.  f.  denoting 10 –15

    femtometer
"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of femto-

< Danish, Norwegian femt ( en ) fifteen + -o-

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.