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a combining form used in the names of units of measure equal to one quadrillion (10 15) of a given base unit:
Origin of peta-
origin uncertain Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for peta-


denoting 1015: petametres, P
Word Origin
C20: so named because it is the SI prefix after tera-; on the model of penta-, the prefix after tetra-
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
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peta- in Medicine

peta- pref.
One quadrillion (1015): petagram.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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peta- in Science
  1. A prefix that means:

  2. One quadrillion (1015), as in petahertz, one quadrillion hertz.

  3. 250 (that is, 1,125,899,906,842,624), which is the power of two closest to a quadrillion, as in petabyte.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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