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 English ≪ Latin < 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.
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
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.

di- in Medicine

di- pref.

  1. Two; twice; double: dichromatic.

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

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.