# 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

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