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oct-

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variant of octa- or octo- before a vowel: octal.
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Other definitions for oct- (2 of 3)

oct.

abbreviation
octavo.

Other definitions for oct- (3 of 3)

Oct.

abbreviation
October.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022

WORDS THAT USE OCT-

What does oct- mean?

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 oktṓ, meaning “eight.” The Latin equivalent, which is almost identical in spelling and pronunciation, is octō.

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 Words That Use entries for both octa- and octo-.

Examples of oct-

One example of a term that features the combining form oct- is octad, “a group or series of eight.” Octad comes from Greek oktás, 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?

Break it down!

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?

How to use oct- in a sentence

British Dictionary definitions for oct- (1 of 2)

Oct

abbreviation for
October

British Dictionary definitions for oct- (2 of 2)

oct-

combining form
(used before a vowel) a variant of octo-
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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