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).

Nearby words

  1. di,
  2. di stéfano,
  3. di-,
  4. di-amelia,
  5. di.,
  6. dia.,
  7. diabase,
  8. diabatic,
  9. diabelli,
  10. diabelli, antonio

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. 2019

British Dictionary definitions for dia-




through, throughout, or duringdiachronic
(in botany) at right anglesdiatropism
in opposite or different directionsdiamagnetism

Word Origin for dia-

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."

Online Etymology Dictionary, © 2010 Douglas Harper

Medicine definitions for dia-




The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Science definitions for dia-


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