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dia- 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, especially before a vowel, di-.

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