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di-1

1.
a prefix occurring in loanwords from Greek, where it meant “two,” “twice,” “double” (diphthong); on this model, freely used in the formation of compound words (dicotyledon; dipolar) and in chemical terms (diatomic; disulfide).
Also, dis-2 .
Compare mono-.
Origin
Middle EnglishLatin < Greek, combining form representing dís twice, double, akin to dýo two. See bi-, twi-

di-2

1.
variant of dis-1. before b, d, l, m, n, r, s, v, and sometimes g and j: digest; divide.

di-3

1.
variant of dia- before a vowel:
diorama.
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for di-

di-1

prefix
1.
twice; two; double dicotyledon
2.
  1. containing two specified atoms or groups of atoms dimethyl ether, carbon dioxide
  2. a nontechnical equivalent of bi-1 (sense 5c)
Word Origin
via Latin from Greek, from dis twice, double, related to duo two. Compare bi-1

di-2

combining form
1.
variant of dia- diopter

dia-

prefix
1.
through, throughout, or during diachronic
2.
across diactinic
3.
apart diacritic
4.
(in botany) at right angles diatropism
5.
in opposite or different directions diamagnetism
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
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Word Origin and History for di-

word-forming element meaning "two, double, twice," from Greek di-, from dis "twice," related to duo (see two).

word-forming element meaning "apart, asunder," form of dis- before certain voiced consonants.

word-forming element meaning "through; thoroughly," form of dia- before vowels.

Online Etymology Dictionary, © 2010 Douglas Harper
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di- in Medicine

di- pref.

  1. Two; twice; double: dichromatic.

  2. Containing two atoms, radicals, or groups: diiodide.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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di- in Science
di-  
A prefix that means "two," "twice," or "double." It is used commonly in chemistry, as in dioxide, a compound having two oxygen atoms.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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