What is the prefix for possible?

There isn't a single specific prefix for "possible". However, depending on the context, you might use these prefixes:

* Im-: Meaning "not" or "lacking" - This creates the opposite, impossible.

* Pot-: Meaning "power" or "strength" - This might create potent or potential, both related to the possibility of something happening.

Let me know if you have a specific scenario in mind, and I might be able to give you a more tailored answer!