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Diplo- is a combining form used like a prefix meaning “double” or “in pairs.” This form is frequently used in scientific terms, especially in zoology and botany.

Diplo- comes from Greek �徱���ó�Dz�, meaning “twofold” or “double-folded.” Distantly related is Latin duplex, which also literally means “twofold.”

What are variants of diplo-?

When combined with words or word elements that begin with a vowel, diplo- becomes dipl-, as in diploid.

One example of a term that features diplo- you may have seen is diplodocus, “a huge herbivorous dinosaur of the genus Diplodocus, growing to a length of about 87 feet.” Diplodocus comes from the New Latin Diplodocus, which uses the equivalent of the form diplo-.

Dippy was revealed to the public in 1905 and he became an instant star. Hear from the Diplodocus himself as he shares some of his memorable moments from the Museum Archives.

— Natural History Museum (@NHM_London)

As we know, diplo- means “double,” while the -docus part of diplodocus means “beam, bar, shaft,” from Greek dokós. Diplodocus literally translates to “double beams,” a reference to the double row of bones in its tail.

What are some words that use the combining form diplo- or dipl-?

• diplobiont
• diplocardia
• diplogenesis
• diploid
• diplomyelia
• diplophase
• diplophonia (using the equivalent form of diplo- in Latin)

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

• dep.
• di-
• pleo-

Not every word that begins with the letters diplo- is necessarily using the combining form diplo- to mean “double.” Diploma and diplomatic are two such examples. Both of these words, as it happens, ultimately come from the same root as diplo-, but they aren’t using diplo- as a combining form. Learn why diploma is a type of document and why diplomatic means “tactful” at our entry for each word.

In suffix -oid means “resembling, like.” With this in mind, what does diploid mean?