# 4th Grade Geometry

## 43 terms · Chapter 12-Geometry vocabulary

### point

an exact location in space

### ray

A part of a line; it has one endpoint and continues without end in one direction

### line

An undefined term; description: A straight path of points in a plane that continues without end in both directions with no endpoints.

### plane

A flat surface that extends without end in all directions

### line segment

A part of a line that includes two points called endpoints and all the points between them

### angle

A figure formed by two line segments or rays that share the same endpoint

### vertex

The point at which two rays of an angle or two or more line segments meet in a plane figure, or where three or more sides meet in a solid figure.

### protractor A tool for measuring the size of an angle

A tool for measuring the size of an angle

### degree (°)

The unit used for measuring angles and temperatures.

### right angle

An angle that forms a square corner and has a measure of 90°

### acute angle

An angle that measures greater than 0° and less than 90°.

### obtuse angle

An angle that measures greater than 90° and less than 180°.

### straight angle

An angle whose measure is 180°.

### diagonal line

A line segment joining nonadjacent vertices of a polygon.

### rotation (turn)

A movement of a figure to a new position by rotating the figure around a point

### intersecting lines

Lines that cross each other at exactly one point

### parallel lines

Lines in the same plane that never intersect and are always the same distance apart.

### perpendicular lines

Two lines that intersect to form four right angles

### polygon

A closed plane figure with straight sides. Each side is a line segment.

### pentagon

A polygon with five sides

### triangle

A polygon with three sides

### hexagon

A polygon with six sides.

### quadrilateral

A polygon with four sides

### octagon

A polygon with eight sides

### regular polygon

A polygon that has sides that are the same length

### congruent

Having the same size and shape

### equilateral triangle

A triangle with 3 equal, or congruent, sides.

### isosceles triangle

A triangle with two equal, or congruent, sides.

### scalene triangle

A triangle with no equal, or congruent, sides.

### right triangle

A triangle with one right angle

### acute triangle

A triangle with three acute angles.

### obtuse triangle

A triangle with one obtuse angle.

### parallelogram

A quadrilateral whose opposite sides are parallel and equal, or congruent.

### rhombus

A parallelogram with four equal, or congruent, sides.

### trapezoid

A quadrilateral with exactly one pair of parallel sides

### Venn diagram

A diagram that shows relationships among sets of things

### two-dimensional

Measured in two directions, such as length and width

### triangular prism

A solid figure that has two triangular bases and three rectangular faces.

### three-dimensional

Measured in three directions, such as length, width, and height

### face

A polygon that is a flat surface of a solid figure

### cube

A solid figure with six congruent square faces

### edge

The line segment where two or more faces of a solid figure meet.

### rectangular prism

A solid figure in which all six faces are rectangles