Prefix · three
Signals three: triangle, trilogy, tricycle, triathlon, tripod, trimester.
Written by Bryan López, English teacher · Updated
Tri- comes from Greek "tri-" and Latin "tres" (three) and signals exactly the number three: triangle = a geometric shape with three angles and three sides; trilogy = a series of three related works; tricycle = a vehicle with three wheels; triathlon = a competition of three disciplines (swimming, cycling, and running); trimester = a period of three months.
In chemistry, tri- signals three atoms or groups of an element: trioxide = a compound with three oxygen atoms (SO₃ = sulfur trioxide). In music: trio = an ensemble of three musicians. In politics: triumvirate = a government of three people. Tri- is a versatile prefix, identical in Spanish and English.
Attaches to nouns and adjectives. Identical in Spanish and English:
Pronunciation: /traɪ/, rhymes with "try." Identical in Spanish and English.
tri-/traɪ/
Tap the button to hear how the prefix sounds. Each word in the table has its own audio.
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.
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
Tri- = "three": triangle = three angles, tricycle = three wheels, trilogy = three works, triathlon = three sports, trimester = three months. Identical in Spanish and English. Remember the sequence: mono- (1), bi- (2), tri- (3), quad- (4), penta- (5).
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?
The prefix tri- signals three: triangle, trilogy, tricycle, triathlon, tripod, trimester. In Spanish it usually maps to tri-.
The prefix tri- is pronounced /traɪ/. For example, "triangle".
"angle" becomes "triangle". It is a typical example of the tri- prefix.
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