angle, angu-

(Latin: a corner, a bend)

triangular (try-ANG-you-luhr) (adjective), more triangular, most triangular
Involving three parties or elements having three aspects: There was a triangular mother-father-child relationship in little Joe's family.
triangularis (try-ANG-you-LAHR-iss) (s) (noun), triangulares (pl)
A facial muscle associated with frowning: For some unexplainable reason, Jackson lost his ability to show his disapproval with any facial expressions because his triangularis would not let his face function in a normal way.
triangulate (try-ANG-you-late) (verb), triangulates; triangulated; triangulating
1. To measure by using trigonometry: Using knowledge of his high school math, Harry was able to triangulate the mountain and determine the height of the cliff he was considering climbing up to.
2. To determine a distance or location by measuring the distance between two points whose exact locations are known and then measuring the intersection between each point and a third unknown point: The map makers were triangulating the countryside so the firemen could locate the precise locations of many homes and other large buildings more precisely.
triangulation (try-ANG-you-lay-shun) (s) (noun), triangulations (pl)
The tracing and measurement of a series or network of triple geometric configurations in order to survey and map out a territory or region: Triangulation today is used for many purposes, including surveying, navigation, metrology, astrometry, binocular vision, and even model rocketry.
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