di-

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).

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

1. variant of dia- before a vowel: diorama.

prefix

1. twice; two; doubledicotyledon
2. 1. containing two specified atoms or groups of atomsdimethyl ether; carbon dioxide
   2. a nontechnical equivalent of bi- 1 (def. 5c)

combining form

1. variant of dia- diopter

1

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

2

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

3

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

pref.

1. Two; twice; double:dichromatic.
2. Containing two atoms, radicals, or groups:diiodide.

1. A prefix that means “two,” “twice,” or “double.” It is used commonly in chemistry, as in dioxide, a compound having two oxygen atoms.