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Rheo- is a combining form used like a prefix meaning “flow,” “current,” or “stream.” It is often used in scientific terms, especially those referring to electrical currents or the flow of fluids in the body.

Rheo- comes from the Greek ����é�Dz�, meaning “stream.”

Rheo- is closely related to another combining form, -rrhea, meaning “flow” or “discharge,” which is connected to—you guessed it—the word diarrhea.

Want to know more? Read our 51�Թ�s That Use -rrhea article.

A scientific term that features the combining form rheo- is rheometer, an instrument used for measuring the flow of fluids, especially blood.

The meaning rheometer becomes clearer when you break it down: rheo- means “flow.” The combining form –meter means “measure.” So, a rheometer literally translates to “flow measurer.”

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

• rheobase
• rheology
• rheopexy
• rheoreceptor
• rheotaxis

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

• -rhea
• -rrhea
• rhod-
• rhodo-
• rhin-
• rhino-

Some fish and amphibians have special, sensory-related organs, rheoreceptors, that help them navigate their environments. Based on the meaning of rheo-, what do rheoreceptors pick up on (are stimulated by)?