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

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

What are variants of octo-?

When combined with words or word elements that begin with a vowel, octo- becomes oct-, as in octane. Another variant of octo- is octa-, as in octastyle. Want to know more? Check out our 51�Թ�s That Use entries for both oct- and octa-.

An example of a word you may have encountered that features octo- is octopus, an animal “having a soft, oval body and eight sucker-bearing arms, living mostly at the bottom of the sea.” Octopus comes from Greek �ǰ��ṓpous, which uses the equivalent of the form octo-.

The octo- portion of the word means “eight,” but the -pus part means “footed,” from Greek ���ú��. Octopus literally translates to “eight-footed.”

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

• octocentenary
• octofoil
• octogenarian (using the equivalent form of octo- in Latin)
• octometer
• octonary (using the equivalent form of octo- in Latin)
• octosyllable (using the equivalent form of octo- in Latin)

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

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

Centenary means “a period of 100 years.” With this in mind, what is an octocentenary?