Related to the sun:
* Heliosphere: The region of space dominated by the sun's magnetic field.
* Heliocentric: Having the sun as the center, as in the heliocentric model of the solar system.
* Heliograph: A device that uses sunlight to transmit signals.
* Heliomagnetism: The study of the sun's magnetic field.
* Helioseismology: The study of the sun's internal structure through its vibrations.
* Heliophysics: The study of the sun and its effects on the solar system.
Other words:
* Helicopter: A type of aircraft that uses rotating blades for lift. (Note: The "helio" part in this word is not related to the sun. It comes from a different Greek word meaning "spiral".)
* Heliochrome: A type of early color photography.
This is not an exhaustive list, but it gives you a good idea of the range of words using the root "helio."