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a combining form meaning “three,” used in the formation of compound words: triacid; triatomic.
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Origin of tri-

Middle English <Latin, combining form representing Latin trēs, tria,Greek treîs, tríathree
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022


What does tri- mean?

Tri- is a combining form used like a prefix meaning “three.” Tri- is often used in a great variety of both everyday and technical terms.

Tri- ultimately comes from both Greek treîs, tría and Latin trēs, tria, all of which mean “three.”

Examples of tri-

An example of a word you may have encountered that features tri- is trident, “a three-pronged instrument or weapon.” The word trident comes from Latin tridēns, which uses the equivalent of the form tri- in the language.

The tri- part of the word means “three,” while the -dent part means “tooth.” Trident literally translates to “three teeth” or “three-toothed.”

Tri- also features in common words such as triangle and tricycle. Learn more about the origins of these words at their entries.

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

The following words use the equivalent forms of tri- in Latin or Greek:

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

Not every word that begins with the letters tri- is necessarily using the combining form tri- to denote “three.” Learn why triage literally means “sorting” at our entry for the word.

Break it down!

Tripods are stands used for holding cameras and telescopes in place. The combining form -pod refers to  “foot.” With this in mind, what does tripod literally mean?

How to use tri- in a sentence

British Dictionary definitions for tri-


three or thricetriaxial; trigon; trisect
occurring every threetrimonthly

Word Origin for tri-

from Latin trēs, Greek treis
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 tri-


Containing three atoms, molecules, or groups:triacetic acid.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.