Definitions for dia-
Random House Webster's College Dictionary
a prefix occurring orig. in loanwords from Greek, with the meanings “through, across, from point to point” (diachronic; diameter; diarrhea), “in different directions, apart, at an angle” (dialysis; diastole ), “completeness or thoroughness (of the action of the verb)” (diagnosis).
Ref: Also, esp. before a vowel, di-. 5 3
Origin of dia-:
< Gk, comb. form repr. diá (prep.) through, across, akin to dýotwo and di-di -1
Origin: From prefix δια-, from διά
alt. of Di-