# Nouns denoting two and three dimensional shapes

- outer boundary
- the outside boundary or surface of something

- perpendicular
- a straight line at right angles to another line

- spiral
- a plane curve traced by a point circling about the center but at increasing distances from the center

- intrados
- the interior curve of an arch

- sinusoid
- the curve of y=sin x

- loop
- anything with a round or oval shape (formed by a curve that is closed and does not intersect itself)

- figure eight
- a two-dimensionsal figure having the shape of the number eight

- complementary angles
- two angles whose sum is a right angle

- spherical triangle
- a spherical polygon formed by the arcs of 3 great circles

- corner
- a small concavity

- prismoid
- a prismatoid whose bases are polygons having the same number of sides and whose other faces are trapezoids or parallelograms

- oblique triangle
- a triangle that contains no right angle

- impression
- a concavity in a surface produced by pressing

- symmetry
- balance among the parts of something

- column
- anything that approximates the shape of a column or tower

- tree
- a figure that branches from a single root

- projection
- any solid convex shape that juts out from something

- equilateral triangle
- a three-sided regular polygon

- lower bound
- (mathematics) a number equal to or less than any other number in a given set

- corrugation
- a ridge on a corrugated surface

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