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dia-

  1. a prefix occurring in loanwords from Greek (diabetes; dialect) and used, in the formation of compound words, to mean “passing through” (diathermy), “thoroughly,” “completely” (diagnosis), “going apart” (dialysis), and “opposed in moment” (diamagnetism).
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Also especially before a vowel, di-.

Origin of dia-

< Greek, combining form representing diá (preposition) through, between, across, by, of, akin to dýo two and di- di-1
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for dia-

dia-

di-

prefix
  1. through, throughout, or duringdiachronic
  2. acrossdiactinic
  3. apartdiacritic
  4. (in botany) at right anglesdiatropism
  5. in opposite or different directionsdiamagnetism
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Word Origin

from Greek dia through, between, across, by
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

Word Origin and History for dia-

before vowels, di-, word-forming element meaning "through, thoroughly, entirely," from Greek dia-, from dia "through, throughout," probably from the root of duo "two" (see two) with a base sense of "twice."

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Online Etymology Dictionary, © 2010 Douglas Harper

dia- in Medicine

dia-

pref.
  1. Through:diapedesis.
  2. Across:diameter.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

dia- in Science

dia-

  1. A prefix meaning “through” or “across,” as in diameter, the length of a line going through a circle.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.