* Heptagon: A polygon with seven sides.
* Heptameter: A line of poetry consisting of seven metrical feet.
* Heptachord: A scale or musical system with seven notes.
* Heptahydrate: A chemical compound containing seven water molecules.
* Heptalogy: A series of seven books or chapters.
* Heptachromatism: The ability to see seven colors of the rainbow (sometimes used figuratively).
* Heptavalent: In chemistry, having seven valence electrons.
* Heptahedron: A geometric solid with seven faces.
Let me know if you would like to know more about any of these words!