Wikipedia says they are synonymous.
Ionization energy is how much energy it takes to abstract an electron from an atom. A molecule with a low ionization energy can more easily be ionized. It seems weird to call this a low ionization potential though. You are trying to say it can easily be ionized, but you would call that a "low ionization potential"? That makes it sound like it ISN'T easy to ionize it.
So, are they the same thing or are they opposites?
Also, why does IE decrease down a group? The explanation given is that the electrons are further from the nucleus. But Z(effective) increases down a group. Who cares if they are further away if they are feeling more charge from the nucleus?