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).

Origin of dia-

<Greek, combining form representing diá (preposition) through, between, across, by, of, akin to dýotwo and di-di-1
  • Also especially before a vowel, di-.

Words Nearby dia-

Other definitions for dia. (2 of 2)


  1. diameter.

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2024

How to use dia- in a sentence

  • A pesar de la caida de Valencia, parece claro al mundo, que las cosas del enemigo estan andando de pejor a pejor cada dia.

    Wanderings in South America | Charles Waterton
  • Diabolus dicitur a dia, quod est duo, et bolos morsus; quasi dupliciter mordens; quia ldit hominem in corpore et anima.

  • (meaning your substance): which is an exact translation of the equally common Irish wish Go medaighe Dia dhuit.

  • The established derivation of Aphrodite dia ten tou athrou genesin may be accepted on the authority of Hesiod.

    Cratylus | Plato

British Dictionary definitions for dia-


  1. through, throughout, or during: diachronic

  2. across: diactinic

  1. apart: diacritic

  2. (in botany) at right angles: diatropism

  3. in opposite or different directions: diamagnetism

Origin of 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

Scientific definitions for dia-


  1. 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.