atto-


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atto-

pref.
One quintillionth (10-18): attotesla.

[From Danish or Norwegian atten, eighteen, from Old Norse āttjān; see oktō(u) in Indo-European roots.]
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.

atto-

prefix
denoting 10–18: attotesla. Symbol: a
[from Norwegian, Danish atten eighteen]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014

atto-

a combining form denoting one-quintillionth (10−18) the size of the unit denoted by the second element of the compound: attosecond.
[< Dan or Norwegian att(en) eighteen + -o-]
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.

atto-

A prefix meaning a quintillionth (10-18). For example, 1 attometer = 1 quintillionth of a meter.
Dictionary of Unfamiliar Words by Diagram Group Copyright © 2008 by Diagram Visual Information Limited