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a combining form meaning “the earth,” used in the formation of compound words: geochemistry.
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Origin of geo-

<Greek geō-, combining form of the earth

Other definitions for geo- (2 of 2)


Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023


What does geo- mean?

Geo- is a combining form used like a prefix meaning “earth.” It is often used in scientific terms in a variety of fields. In some rare instances, such as the term geocode, geo- is used as an abbreviation of geographical.

Geo- comes from Greek , meaning “earth.” A synonym of is khthṓn, which is the source of several words related to the underworld, such as chthonic.

What are variants of geo-?

When combined with words or word elements that begin with a vowel, geo- becomes ge-, as in geanticline. Want to know more? Read our Words That Use article for ge-.

Examples of geo-

An example of a word you have likely encountered that features geo- is geology, “the science that deals with the dynamics and physical history of the earth.”

We know geo- means “earth,” so the -logy portion of the word? That’s right, -logy refers to “study,” from the Greek logía. Geology literally translates to “study of the earth.”

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

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

Not every word that begins with the exact letters ge-, such as gearbox or geoduck, is necessarily using the combining form ge- to denote “earth.” Learn why geoduck is the name of a kind of saltwater clam at our entry for the word.

Break it down!

Given the meaning of geo-, what is another name for the discipline known as geoscience?

How to use geo- in a sentence

British Dictionary definitions for geo- (1 of 2)



/ (ˈdʒiːəʊ) /

noun plural geos or gios
(esp in Shetland) a small fjord or gully

Word Origin for geo

C18: from Old Norse gjā ravine; related to Old English gionian to yawn

British Dictionary definitions for geo- (2 of 2)


combining form
indicating earthgeomorphology

Word Origin for geo-

from Greek, from earth
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

Scientific definitions for geo-


A prefix that means “earth,” as in geochemistry, the study of the Earth's chemistry.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.