| Geometry Vocabulary
We are creating "Geometry Vocabulary" booklets in class. Booklets will start coming home on
February 7. Please have your child spend some time each night practicing the meaning of these
terms. This will also help your child as he/she works on their geometry mobile.
1) plane figure - a figure that lies on a plane; flat
2) 1 dimensional figure - an object measured in 1 direction (length)
3) line - a straight path on a plane, that goes on and on in 2 directions
line segment - a part of a line with 2 endpoints
4) ray - a part of a line with endpoint that goes on and on in 1 direction
5) parallel lines - 2 lines that are the same distance apart
6) intersecting lines - lines that cross and meet at exactly 1 point
7) perpendicular lines - lines that cross or meet to form right angles
8) straight angle - rays that share a common endpoint and form a 180 degree angle (straight line)
9) right angle - measures exactly 90 degrees; a “perfect” corner
10) obtuse angle - larger or open wider than a right angle
11) acute angle - smaller than a right angle (“a cute little angle”)
12) 2 dimensional figure - an object measured by length and width
13) vertex/vertices - the point where 2 line segments meet in 2D objects, or where 3 faces
meet in 3D objects
14) side - the line segments that make up a 2D object
15) polygon - a closed plane (flat) figure with straight sides
16) circle - a curved plane figure with each point on the curved line being the same
distance from its center point
17) quadrilateral - any polygon with 4 sides and 4 angles; There are 6 types: square,
rectangle, parallelogram, rhombus, trapezoid, and a general quadrilateral
18) square - a polygon (quadrilateral) with 4 congruent sides and 4 right angles; its
opposite sides are parallel and congruent
19) triangle - a polygon with 3 sides, angles, and vertices
20) rectangle - a polygon (quadrilateral) with 4 right angles, whose opposite sides are
parallel and congruent
21) parallelogram - a polygon (quadrilateral) whose opposite sides are parallel and
congruent (2 pairs of parallel sides)
22) rhombus - a parallelogram (quadrilateral) whose 4 sides and opposite angles are
congruent
23) trapezoid -a quadrilateral (quadrilateral) with only 1 pair of parallel sides
24) pentagon - a polygon with 5 sides, angles, and vertices
25) hexagon - a polygon with 6 sides, angles, and vertices
26) octagon - a polygon with 8 sides, angles and vertices
27) 3 dimensional figure - measured in 3 directions: length, width, and height
28) edge - the line segment where 2 faces meet
29) face - the flat surfaces that makes up a 3D figure
30) sphere - a 3D object with 1 curved surface
31) cube - a 3D object with 6 congruent square faces
32) rectangular prism - a 3D object with 6 rectangular faces
33) triangular prism - a 3D object with 2 triangular and 3 rect. faces
34) pyramid - ”spear-a-mid” 3 types: square, rectangular, triangular.
35) cylinder - has 2 flat faces and 1 curved surface; examples: tissue rolls, cans
36) cone - has 1 flat face and 1 curved surface; examples: party hats, ice cream cones
37) symmetry/lines of symmetry - a figure has a line of symmetry if it can be folded where
the one half is an exact fit on top of the other; a square has 4 lines of symmetry
38) congruent - same size and shape
39) transformation - the movement of any shape in geometry; 3 types: reflection,
translation, rotation
40) reflection - when 1 shape makes the mirror image of another shape; flip
41) translation - when 1 shape slides into another position; slide
42) rotation - when 1 shape turns around a point; turn
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How many names can you think of for a square? Can you name seven?
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rectangle
quadrilateral
polygon
2 dimensional
plane figure
parallelogram
rhombus
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