Here are some examples of how "dia-" is used as a prefix:
* Diameter: The distance across a circle through its center.
* Diagonal: A line segment connecting two non-adjacent vertices of a polygon.
* Dialogue: A conversation between two or more people.
* Diagnosis: The identification of a disease or condition.
* Diaphanous: Transparent or translucent.
* Diarrhea: Frequent loose stools.
* Diaspora: The dispersion of people from their homeland.
The specific meaning of "dia-" can vary depending on the word it is used in, but it always conveys the idea of movement, separation, or passing through.