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Geometry vocabulary words for students

This list supports middle and high school students studying geometry, covering the basic terms needed to describe shapes, angles, lines, and measurement. Use it to preview vocabulary before a unit, review for a test, or talk through a proof or diagram with a study partner.

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Geometry vocabulary words for students

30 words
WordMeaningIn a sentenceSave
anglenounA figure formed by two rays that start at the same point, or the measure of the turn between them.The two rays form a right angle.
vertexnounThe point where two or more lines or edges meet, such as the corner of an angle or shape.Each triangle has three vertices, the points where its sides intersect.
paralleladjectiveDescribing straight lines in the same plane that never meet, however far they extend.Opposite sides of a rectangle are parallel.
perpendicularadjectivePositioned at an exact right angle, ninety degrees, to another line or surface.The carpenter checked that the wall was perpendicular to the floor before installing shelves.
polygonnounA closed, flat shape with three or more straight sides.A triangle is a polygon with three sides.
trianglenounA geometric shape with three straight sides and three angles.The teacher drew a triangle on the board to explain its three angles.
quadrilateralnounA polygon with exactly four sides and four angles.Squares, rectangles, and trapezoids are all examples of a quadrilateral.
hypotenusenounThe longest side of a right triangle, located opposite the right angle.By the Pythagorean theorem, the square of the hypotenuse equals the sum of the squares of the other two sides.
congruentadjectiveHaving exactly the same size and shape, so that one figure matches another perfectly.The two triangles are congruent because their corresponding sides and angles are equal.
similaradjectiveAlike in one or more ways without necessarily being identical.The two coats are similar in color but different in length.
symmetrynounThe quality of having balanced, matching proportions on either side of a dividing line or point.The butterfly's wings show near-perfect symmetry in their color and pattern.
radiusnounA line segment from a circle's center to its boundary, or the length of that segment.The radius of a circle with diameter 12 centimeters is 6 centimeters.
diameternounA line segment across a circle through its center, or the length of that segment.Draw a diameter through the center of the circle.
circumferencenounThe distance around a circle.We wrapped a string around the lid to estimate its circumference.
perimeternounThe total distance around the boundary of a flat shape.The square has sides of 4 centimeters and a perimeter of 16 centimeters.
areanounThe amount of two-dimensional space inside a region or across a surface.A rectangle that is 3 meters by 4 meters has an area of 12 square meters.
volumenounThe degree of loudness of a sound, or the control that adjusts it.Please turn down the volume; the music is too loud for a library.
coordinate planenounA flat surface defined by two perpendicular number lines, used to locate points with ordered pairs.Students plotted each point on the coordinate plane using its x and y values.
line segmentnounA straight part of a line that has two distinct endpoints and a definite length.The diagram showed a line segment connecting point A to point B.
raynounA narrow beam of light, heat, or other radiation traveling in a straight line from its source.A single ray of sunlight broke through the clouds and lit up the valley below.
obtuseadjectiveSlow to understand things that are obvious to other people; also, an angle greater than 90 degrees.He seemed deliberately obtuse, ignoring every hint that his plan wouldn't work.
acuteadjectiveVery serious, severe, or intense, especially describing a problem, feeling, or sensation.The refugees faced an acute shortage of clean drinking water.
right anglenounAn angle of exactly ninety degrees, formed where two lines meet perpendicularly.The corners of a standard sheet of paper each form a right angle.
equilateraladjectiveHaving all sides of equal length, especially describing a triangle.An equilateral triangle has three equal sides and three sixty-degree angles.
isoscelesadjectiveDescribing a triangle that has exactly two sides of equal length and two equal angles.The students measured the isosceles triangle to confirm that two of its sides matched.
scaleneadjectiveDescribing a triangle in which all three sides and all three angles are of different measures.The teacher drew a scalene triangle on the board to contrast it with an equilateral one.
diagonaladjectiveRunning in a straight, slanting direction rather than horizontally or vertically, especially between two opposite corners.The bishop in chess can only move along a diagonal line across the board.
tangentnounA straight line that touches a curve at one point without crossing into it, especially in geometry.The engineer calculated the tangent to the circle at the exact point where the road curved away.
bisectornounA line, ray, or plane that divides an angle or line segment into two equal parts.The teacher drew a bisector through the angle to split it into two equal halves.
transformationnounA complete and often dramatic change in form, appearance, or character.The caterpillar's transformation into a butterfly amazed the young students.

Describing shapes and angles

Geometry vocabulary often starts with basic building blocks like vertex, line segment, and ray, which combine to form angles and polygons. Words such as obtuse, acute, and right angle describe the size of an angle, while congruent and similar describe whether two shapes match exactly or share the same proportions.

Frequently asked questions

What are basic geometry vocabulary words?

Basic geometry vocabulary includes words like angle, vertex, polygon, perimeter, and area, which describe the shapes and measurements studied in a typical geometry course.