What is a word that has hepta prefix not heptagon?

The prefix "hepta" means "seven". Here are a few words with the "hepta" prefix that are not "heptagon":

* Heptachord: A seven-note musical scale.

* Heptameter: A line of poetry containing seven metrical feet.

* Heptavalent: Having a valence of seven.

* Heptahydrate: A chemical compound containing seven water molecules.

* Heptalogy: A series of seven books.

* Heptachromatic: Having seven colors.

* Heptamerous: Having seven parts.

Let me know if you'd like more examples!