tri-, tre-

(Greek > Latin: a numerical prefix meaning, three, thrice, threefold; triple; a word element for number 3)

Triangulum (try-ANG-you-lum) (s) (noun) (no plural)
An ancient constellation shaped like an equilateral form with three equal sides: Between the constellations Andromeda and Aries there is a Triangulum.

Triangulum is a small constellation in the northern sky. Its name is Latin for "triangle", derived from its three brightest stars, which form a long and narrow triangle. Known to the ancient Babylonians and Greeks, Triangulum was one of the 48 constellations listed by the 2nd century astronomer Ptolemy.

— Source: Wikipedia
1. Occurring every three years; lasting for three years; equal to triennial.
2. Occurring three times a year.
Having three flowers.
Having three apses, as most Greek churches.
The ruler of one of three divisions of a country or territory.
1. The government or jurisdiction of a triarch; one of three divisions of a country ruled by triarchs.
2. Government by three rulers or powers jointly; three persons associated in government, a triumvirate.
3. A group of three districts or divisions of a country each under its own ruler.
In geology, the lowest of three major divisions of fossiliferous rocks which together make up the Mesozoic or Secondary series, namely: Triassic; Jurassic; and Cretaceous.

It lies above the Permian and below the Jurassic.

triathlon (s) (noun), triathlons (pl)
An intense athletic-endurance competition in which all participants must swim, ride a bicycle, and run particular distances without stopping between each of the events.
A figure or utensil with three arms, especially a three-branched flint.
A deformed fetus, usually conjoined twins, having three arms.
In botany, having three bracts.
Tribus unum.
From three, one.

Motto of Trinity University, San Antonio, Texas, USA.

A reference to a legislature composed of three chambers.
1. Pertaining to thirty years.
2. Consisting of thirty years.
3. Occurring once in every thirty years.
4. Etymology: from Latin tricennium, "thirty years"; from triginta "thirty" + annus, "year" (tricennalis).
A person who is three-hundred years old.

Cross references of word families that are related, partially or totally, to: "three, third": terce-; terti-; trigono-; trito-.