What's the derivation of the word "Isotope"?

Where does the word "Isotope" actually come from? I think it's the Greek "Iso" which means "equal" but what about "tope"? What does that mean? Does anyone know? I'm looking for a way of remembering what an isotope of an element is, and, unusually, I can't seem to find where the word originally came from. Many thanks.