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Dec- is a combining form used like a prefix meaning “ten.” It appears in a small range of terms.

Dec- comes from the Greek ��é�첹, meaning “ten.” The word December is related to this root via the Latin equivalent, decem. In fact, what is now the twelfth month of the year was once the tenth month of the early Roman calendar. Learn more at our entry for December.

What are variants of dec-?

Dec- is a variant of deca-, which loses its –a– when combined with words or word elements beginning with vowels. A similar prefix is deka-, which is reserved for the naming of metric units, and a related Latin-origin form is deci-, from Latin decimus, “t��Գٳ�.”

Want to know more? Check out our �y��vlogs That Use articles for deca-, deci-, and deka-.

An example of a term you may have come across that features dec- ������decade, “a period of ten years.” Decade comes from the Greek dekad-, which features the equivalent of the form dec-.

The form dec- means “ten,” as we have seen. The suffix -ade has various meanings, including denoting “a group or unit comprising a certain number, sometimes of years.” Decade literally translates to “a group of ten [years].”

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

• decandrous
• decathlon
• decennary (using the equivalent form of dec- in Latin)
• decennium (using the equivalent form of dec- in Latin)

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

• dactylo-
• de-
• deci-
• deka-
• dextro-
• dodeca-

Not every word that begins with the letters dec-, such as decadence or decapitate, is necessarily using the combining form dec- to denote “ten.” Learn why decadence is related to “decay” at our entry for the word.

A biathlon is an athletic contest comprising two different events, typically skiing and shooting. A triathlon is an athletic contest comprising three different events. In keeping with this pattern, what is a decathlon?