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Octa- is a combining form used like a prefix meaning “eight.” It is often used in a great many scientific and technical terms.

Octa- comes from Greek �ǰ��ṓ, meaning “eight.” The Latin equivalent, which is almost identical in spelling and pronunciation, is �dz���ō.

What are variants of octa-?

When combined with words or word elements that begin with a vowel, octa- becomes oct-, as in octane. Another variant of octa- is octo-, as in octofoil.

Want to know more? Check out our 51�Թ�s That Use entries for both oct– and octo-.

An example of a word you may have encountered that features octa- is octagon, “a polygon having eight angles and eight sides.” Octagon comes from Greek �ǰ��á��ō�ԴDz�, which features the equivalent of the form octa-.

We know octa- means “eight,” but what about the -gon portion of the word? The form -gon, from Greek ��ō��í��, means “angled, angular.” Octagon literally translates to “eight-angled.”

What are some words that use the combining form octa-?

• octachord (using the equivalent form of octa- in Greek)
• octahedron (using the equivalent form of octa- in Greek)
• octameter (using the equivalent form of octa- in Greek)
• octastyle
• octavalent

What are some other forms that octa- may be commonly confused with?

• oc-
• oculo-
• ocy-
• oleo-
• ont-
• onto-
• opto-
• oto-
• oxo-

The combining form -hedron means “face” and is used in the names of geometric figures with a certain number of faces. With this in mind, what is an octahedron?