What does the prefix sis mean?

The prefix "sis" doesn't exist as a standalone prefix in English. It's likely you're thinking of "sys-", which is a prefix meaning "together" or "with".

Here are some examples:

* System: A group of interacting or interdependent elements forming a complex whole.

* Synthesis: The combination of parts to form a whole.

* Synergy: The interaction of two or more agents or forces so that their combined effect is greater than the sum of their individual effects.

* Symbiosis: Interaction between two different organisms living in close physical association, typically to the advantage of both.

Let me know if you have any other prefixes you'd like to understand!