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).

prefix

1. through, throughout, or duringdiachronic
2. acrossdiactinic
3. apartdiacritic
4. (in botany) at right anglesdiatropism
5. in opposite or different directionsdiamagnetism

before vowels, di-, word-forming element meaning “through, thoroughly, entirely,” from Greek dia-, from dia “through, throughout,” probably from the root of duo “two” (see two) with a base sense of “twice.”

pref.

1. Through:diapedesis.
2. Across:diameter.

1. A prefix meaning “through” or “across,” as in diameter, the length of a line going through a circle.