51�Թ�

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

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

What are variants of oct-?

Oct- is a variant of octa- or octo-, which loses its –a– or –o– when combined with words or word elements beginning with vowels.

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

One example of a term that features the combining form oct- is octad, “a group or series of eight.” Octad comes from Greek �ǰ��á��, which uses the equivalent of the form oct-.

The form oct- means “eight,” while the -ad portion of the word is a suffix denoting “a group or unit.” Octad literally translates to “a group of eight.”

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

• octane
• octave (using the equivalent form of oct- in Latin)
• octennial (using the equivalent form of oct- in Latin)
• octet
• octillion (using the equivalent form of oct- in French)

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

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

A duet is a musical composition for two voices or instruments. The du- part of the word means “two.” With this in mind, what is an octet?