κρύσταλλος

Normally, the ice we find on Earth is frozen water. This is not the case in general: e.g. on other planets of the solar system or on comets that are far away from the Sun, also other substances are frozen (or liquid) although they are typically gases on Earth (e.g. CO2, CO, methane).

However, for Aristotle and his successors, the term "ice" typically meant frozen water.