Webster's Revised Unabridged Dictionary · 1913

Dia-

Dia-

[Greek dia` through; orig., dividing into two parts; akin to {not transcribed} two. See Two, and compare 1st Di-.]

A prefix denoting through; also, between, apart, asunder, across. Before a vowel dia- becomes di-; as, diactinic; dielectric, etc.

Also: Di-