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The Collaborative International Dictionary of English v.0.48 (gcide)

Triangle \Tri"an`gle\, n. [L. triangulum, fr. triangulus
triangular; tri- (see {Tri-}) angulus angle: cf. F.
triangle. See {Angle} a corner.]
1. (Geom.) A figure bounded by three lines, and containing
three angles.
[1913 Webster]

Note: A triangle is either plane, spherical, or curvilinear,
according as its sides are straight lines, or arcs of
great circles of a sphere, or any curved lines
whatever. A plane triangle is designated as scalene,
isosceles, or equilateral, according as it has no two
sides equal, two sides equal, or all sides equal; and
also as right-angled, or oblique-angled, according as
it has one right angle, or none; and oblique-angled
triangle is either acute-angled, or obtuse-angled,
according as all the angles are acute, or one of them
obtuse. The terms scalene, isosceles, equilateral,
right-angled, acute-angled, and obtuse-angled, are
applied to spherical triangles in the same sense as to
plane triangles.
[1913 Webster]

2. (Mus.) An instrument of percussion, usually made of a rod
of steel, bent into the form of a triangle, open at one
angle, and sounded by being struck with a small metallic
rod.
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3. A draughtsman's square in the form of a right-angled
triangle.
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4. (Mus.) A kind of frame formed of three poles stuck in the
ground and united at the top, to which soldiers were bound
when undergoing corporal punishment, -- now disused.
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5. (Astron.)
(a) A small constellation situated between Aries and
Andromeda.
(b) A small constellation near the South Pole, containing
three bright stars.
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{Triangle spider} (Zool.), a small American spider
({Hyptiotes Americanus}) of the family {Ciniflonidae},
living among the dead branches of evergreen trees. It
constructs a triangular web, or net, usually composed of
four radii crossed by a double elastic fiber. The spider
holds the thread at the apex of the web and stretches it
tight, but lets go and springs the net when an insect
comes in contact with it.
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