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Chori- is a combining form used like a prefix meaning either “chorion” or “choroid.” It is used in a few scientific terms, especially in anatomy and biology.

The chorion is the outermost membrane surrounding the embryo of a reptile, bird, or a mammal, and which contributes to the formation of the placenta in mammals, including humans. Choroid means “like the chorion,” but it can also refer to the choroid coat, the vascular layer of the eye.

Chori- comes from the Greek ����ó�����Dz�, meaning “the outer membrane of the fetus.”

Chori– is a variant of chorio-, which loses its –o– when combined with words or word elements beginning with vowels.

Want to know more? Read our 51�Թ�s That Use chorio– article.

Related to chori- are the combining forms choroido- and chorioido-, specifically used to represent the choroid coat.

One example of a scientific term that features chori– is chorioma, also known as choriocarcinoma, meaning “any benign or malignant tumor of chorionic tissue.”

In this case, chori- means “chorion.” The second half of the word, -oma, is a combining form used to name tumors. Chorioma means “chorion tumor.”

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

• cheiro-
• chiro-
• choreo-
• chromo-

In some examples from botany, such as choripetalous, chori- is based on the Greek ����ō��í��, meaning “apart.”

You may be familiar with the suffix -oid, meaning “resembling, like.” Given the meaning of chori-, what does something chorioid resemble?