What does the prefix tri- mean?
Tri- comes from the Latin tres and the Greek tri-, and it shows exactly the number three. It talks about something with three parts, three sides or three units.
ESEN
Prefix · three
tri-
Signals three: triangle, trilogy, tricycle, triathlon, tripod, trimester.
Scientific
Written by Bryan López, English teacher · Updated
Tri- in science, music and politics
Tri- is a very versatile prefix. In chemistry, it shows three atoms or three groups of an element. In music, it names a group of three musicians. In politics, it is used to talk about a government shared by three people. Because it always means "three", there are almost never surprises: if you see it, look for the hidden three.
How it is used
Attaches to nouns and adjectives:
- tri- + shape/groupangle → trianglecycle → tricyclepod → tripodo → trio
- tri- + period/competitionathlon → triathlonmester → trimesterlogy → trilogyumvirate → triumvirate
How it is pronounced
tri-/traɪ/
Tap the button to hear how the prefix sounds. Each word in the table has its own audio.
Examples
Root word
With tri-
In a phrase
- angletriangleA triangle is the strongest geometric shape used in bridges and roofs.
- cycletricycleThe child learned to steer a tricycle before moving to a bicycle.
- logytrilogyThe author spent fifteen years completing the three-book trilogy.
- athlontriathlonShe trained eighteen months to finish her first triathlon.
- podtripodThe photographer used a tripod for the long-exposure night shots.
- mestertrimesterMany schools divide the year into three trimesters.
- oxidetrioxideSulfur trioxide reacts with water to contribute to acid rain.
Common mistakes
trilogy = any series of more than two works
trilogy = exactly three related works that together form a unified whole
A trilogy has exactly three parts: The Lord of the Rings (trilogy), His Dark Materials (trilogy). A series of four is a "tetralogy"; five is a "pentalogy." In informal use, "trilogy" is sometimes loosely applied to any series, but technically it is always exactly three.
triathlon = any endurance competition
triathlon = a specific competition of exactly three disciplines: swimming, cycling, and running
A triathlon always combines the same three disciplines in the same order: swimming, cycling, and running. It exists at various distances: sprint, Olympic, and Ironman. A two-discipline competition would be a "duathlon" (or biathlon in some contexts).
A trick to remember it
Think of a triangle, which has three sides: tri- = three. triangle, tricycle.
Practise what you learned
Exercise 1 · Form the word
Exercise 2 · Pick the right one
"The author spent fifteen years completing the ___, with each novel exploring a different generation."
Exercise 3 · Pick the right one
How many disciplines does a triathlon have, and what are they?
Frequently asked questions
What does the prefix tri- mean in English?
The prefix tri- signals three: triangle, trilogy, tricycle, triathlon, tripod, trimester.
How do you pronounce tri-?
The prefix tri- is pronounced /traɪ/. For example, "triangle".
Can you give an example of a word with tri-?
"angle" becomes "triangle". It is a typical example of the tri- prefix.
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