What does the prefix coni- mean?

The prefix "coni-" is actually a variant of the prefix "con-", which means "with," "together," "jointly," or "in conjunction with."

It's not as commonly used as "con-", but it can be found in some words, such as:

* Coniferous: referring to trees that bear cones (cones are structures that hold seeds together).

* Conjoin: to join together, or to unite.

Keep in mind that the "coni-" prefix is relatively rare and is often considered archaic. In most cases, "con-" is the more standard form.