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Deci- is a combining form used like a prefix meaning “tenth.” It is most often used to denote units of the metric system.

Deci- comes from the Latin decimus, meaning “tenth.” The word decimate, meaning “to destroy a great number or proportion of” comes from this same Latin root. Find out how at our entry for decimate.

A similar word from Greek, ��é�첹, meaning “ten,” gives us the combining forms dec-, deca-, and deci-. Want to know more? Check out our �y��vlogs That Use articles for all three forms.

Despite the similarity between the two forms, it’s important not to confuse deci-, which means “tenth,” with deca-, meaning “ten.” A decigram is one-tenth of a gram (0.1 g), but a decagram is ten grams (10 g).

One example of a technical term you may have encountered that features the combining form deci- is decimeter, “a unit of length equal to 1/10 of a meter.” Decimeter comes from the French ��é������è�ٰ���, which uses the equivalent of the combining form deci-.

The first part of the word, deci-, means “tenth,” as we have seen. The combining form -meter has a variety of meanings, but in this case it refers to the metric unit “meter.” Decimeter literally means “a tenth of a meter.”

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

• decibar
• decibel
• decillion (using the equivalent form of deci- in Latin)
• deciliter (using the equivalent form of deci- in French)
• decimal (using the equivalent form of deci- in Latin)

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

• dactylo-
• de-
• dextro-
• di-
• dodeca-

Not every word that begins with the exact letters dec- or deci-, such as decide and decision, is necessarily using the combining forming deci- to denote “tenth.” Learn where these words come from at our entries for decide and decision.

A liter is a unit used for measuring liquids. With this in mind, what is a deciliter?