An example of dia used as a prefix is in the word "diagnosis," which means a thorough analysis of a disease.
Origin of dia
- ME < OFr < L < Gr dia, through, across < *disa, in two, apart < IE *dis- < base *dwo, two
From Webster's New World College Dictionary, 5th Edition
- Greek from dia through
From American Heritage Dictionary of the English Language, 5th Edition