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Geometry dictionary
A:
Acute angle: an angle less than 90 degrees but more than 0 degrees
Acute triangle: a triangle with 3 acute angles
Altitude: the perpendicular distance from the base
Apothem: it is the distance from the center of a polygon to either of the sides.
Arc: a part of a circle
B:
Base: it is the bottom or the lowest part of a figure.
C:
Circle: set of points
Central angle: an angle whose vertex is on the center of the circle
Centroid : the pt. of concurrency of 3 medians of a triangle.
Circular: a cone or cylinder with circles for base(s)
Circumference: perimeter of a circle
Collinear points: points that lie on the same line
Concave: curved inward like the inner surface of a bowl or sphere;at least one interior angles is greater
than 180˚
Cone: a figure with 2 circular bases
Congruent: two figures’shape and size are the same
Convex: having a surface that curves outward rather than inward; having a surface that curves outward
rather than inward
Cylinder: a figure with two parallel circular bases
Cube: a hexahedron with six equal squares as faces
Converse statement:statement formed by switching the hypothesis and conclusion in a
conditional statmentment.
D
Diagonal: a line segment connecting 2 non-adjacent vertices of a polygon
E
Equilateral angle: a triangle with 3 ≅ angles
Equilateral triangle: a three-sided regular polygon
F
Face: flat surface of a solid
H
Hexagon:6 sided figure
I
Isosceles triangle: a triangle with two equal sides
Inscribed angle: an angle whose vertex is on the circle and whose sides contain the chords of the circle
Intercepted arc: arc that lies in the interior of an inscribed angle and has endpts on the angle
Isosceles trapezoid: a trapezoid with two ≅ legs
K
Kite: a quadrilateral with 2 pair of adjacent congruent sides
L
Lateral area: the sum of the areas of the lateral faces only
Line: a straight geometric element that has length but not width or thickness and whose identity is
determined by two points
Locus: set of all points in a plate that satisfy a given condition or a set of given condition
M
Median : is a line segment joining a vertex to the midpoint of the opposing side
Midpoint:
Midsegment: a segment that connect the midpts. of 2 sides of a triangle
O
Oblique: a 3-d figure with an altitude not perpendicular to the base
Obtuse angle: an angle between 90 and 180 degrees
Obtuse triangle: a triangle with one obtuse angle
Octagon: eight-sided figure
P
Parallel Lines: lines that never intersect in a plane
Parallelogram: a two-dimensional geometric figure formed of four sides in which both pairs of opposite
sides are parallel and of equal length, and the opposite angles are equal
Pentagon: a pentagon is any five-sided polygon
Perpendicular: meeting at a 90˚angle
Perimeter: distance around the given figure
Point of tangency: it’s the pt. at which a tangent line or a segment intersects a circle
Polygons: a closed plane figure bounded by straight sides
Prism: 2 congruent bases in // planes
Probability: a number that represents the chance that an event will occur
Protractor: an instrument shaped like a semicircle marked with the degrees of a circle, used to measure
or mark out angles
Pyramid: it has one base, all of the edges connect at the same vertex.
Q
Quadrilateral: a two-dimensional geometric figure with four sides
R
Radius: a radius (plural: radii) of a circle or sphere is any line segment from its center to its perimeter.
Radius of a polygon: the radius of its circumscribed circle, or the distance from the center to a vertex
Ray: piece of a line with only one endpt and continues forever in the other direction.
A
B
Regular polygon: it is a plane figure that has equal sides
Right angle: the 90 degree angle between two perpendicular lines
Right triangle: a triangle with one right angle
S
Secant: a straight line that intersects with a curve in two or more places
Similar: describes geometric figures that differ in size or proportion but not in shape or angular
measurements
Sphere: it is a round solid figure
Supplementary angles: 2 or more angles that sum to 180˚
Surface: a 3-d geometric figure with polygons or curves for the sides and bases
T
Tangent: a line or a segment that intersects a circle at exactly one pt.
Triangle:3 sided figure
Translation: a slide
Transversal: a line that crosses a pair of parallel line
Trapezoid: a quadrilateral that has two parallel sides
V
Vertex: where 2 edges meet
Vertical angles: ≅ opposite angles formed by 2 intersecting lines
Volume：the amount of space inside the solid.