* Octagon: A polygon with eight sides.
* Octahedral: Having the shape of an octahedron.
* Octahedron: A polyhedron with eight faces.
* Octal: Relating to the base-8 number system.
* Octane: A type of hydrocarbon used as a fuel.
* Octave: An interval of eight notes in music.
* Octopod: An eight-armed cephalopod, such as an octopus.
* Octuple: To multiply by eight.
* Octennial: Occurring every eight years.
* Octogenarian: A person who is 80 years old or older.
There are also some less common words, such as:
* Octachord: A musical scale with eight notes.
* Octastich: A poem consisting of eight lines.
* Octamer: A complex of eight molecules.
This list is not exhaustive, as there are many other technical and scientific terms that use the prefix "octa-".