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Duo- is a combining form used like a prefix meaning “two.” It is occasionally used in technical terms.

Duo- comes from Greek ��ý�� and Latin duo, both meaning “two.” In fact, English’s own word two is related to these roots! Learn more at our entry at two.

One example of a technical term that features the combining form duo- is duotone, “of two tones or colors.”

The combining form duo- means “two,” while -tone here means “color.” Duotone literally translates to “two colors” or “two-colored.”

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

• duobinary
• duopoly
• duotype
• duologue
• duopsony

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

• deoxy-
• di-
• dia-

The combining form duodeno- does not use duo- to mean “two.” Learn why duodeno- represents a part of the small intestine at our entry.

A monologue is the part of a drama in which a single speaker talks at length. With this in mind, what is a duologue, also known as a dialogue?