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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
This entry is located in the following units: angle, angu- (page 3) tri-, tre- (page 2)