di-

WordReference Random House Learner's Dictionary of American English © 2025

di-,¹ prefix. 

1. di- comes from Greek, where it has the meaning "two, double''. This meaning is found in such words as: diode, dioxin, diptych.

Collins Concise English Dictionary © HarperCollins Publishers::

di- prefix

1. twice; two; double: dicotyledon
2. containing two specified atoms or groups of atoms: dimethyl ether, carbon dioxide
3. a nontechnical equivalent of bi-15c

Etymology: via Latin from Greek, from dis twice, double, related to duo two. Compare bi-¹

di- combining_form

1. variant of dia-: diopter

WordReference Random House Learner's Dictionary of American English © 2025

dia-, prefix. 

1. dia- comes from Greek, where it has the meanings "through, across, from point to point;
   completely.'' These meanings are found in such words as: diagnosis, dialogue, dialysis, diameter, diaphanous, diarrhea.

WordReference Random House Unabridged Dictionary of American English © 2025

dia-, 

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).

Also,[esp. before a vowel,] di-. 

• Greek, combining form representing diá (preposition) through, between, across, by, of, akin to dýo two and di- di-¹

dia., 

1. Mathematics diameter.

WordReference Random House Unabridged Dictionary of American English © 2025

di¹  (dē), prep. 

1. Foreign Terms from;
   of: used in Italian personal names, originally to indicate place of origin:
   Conte di Savòia.

Also, Di. 

• Latin dē
• Italian

di²  (dē), n. [Music.]

1. Music and Dance a tone in the ascending chromatic scale between do and re.

• perh. alteration of do²

Di  (dī), n. 

1. Chemistry a female given name, form of Diana. 

DI, 

1. Government Department of the Interior.
2. drill instructor.

Di, [Symbol, Chem.]

1. didymium.

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. Cf. mono-. 

• Greek, combining form representing dís twice, double, akin to dýo two. See bi-, twi-
• Middle English Latin

di-² :

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

di-³ :

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

di., 

1. Mathematics diameter.

Also, dia. 

Collins Concise English Dictionary © HarperCollins Publishers::

dia-, di- prefix

1. through, throughout, or during: diachronic
2. across: diactinic
3. apart: diacritic

Etymology: from Greek dia through, between, across, by