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1. One quadrillion (1015): petahertz.
2. 1,125,899,906,842,624 (250): petabyte.
[Alteration of penta-from its representing the fifth power of a thousand).]
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.
(Units) denoting 1015: petametres. Symbol: P
[C20: so named because it is the SI prefix after tera-; on the model of penta-, the prefix after tetra-]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
a combining form used in the names of units of measure equal to one quadrillion (1015) of a given base unit.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.