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a combining form meaning “flow,” “current,” “stream,” used in the formation of compound words: rheoscope.
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“Was” is used for the indicative past tense of “to be,” and “were” is only used for the subjunctive past tense.
Compare -rrhea.

Origin of rheo-

Combining form representing Greek rhéosstream, something flowing
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022


What does rheo- mean?

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 rhéos, 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 Words That Use -rrhea article.

Examples of rheo-

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-?

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

Break it down!

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)?

British Dictionary definitions for rheo-


combining form
indicating stream, flow, or currentrheometer; rheoscope

Word Origin for rheo-

from Greek rheos stream, anything flowing, from rhein to flow
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Medical definitions for rheo-


Current; flow:rheotaxis.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.