# Fourth Grade Module 4 Vocabulary

Terminology
New or Recently Introduced Terms

  Acute angle (angle with a measure of less than 90°)

Acute triangle (triangle with all interior angles measuring less than 90°)

Adjacent angle (Two angles ∠𝐴𝑂𝐶 and ∠𝐶𝑂𝐵, with a common side 𝑂𝐶 ⃑⃑⃑⃑⃑ , are adjacent angles if 𝐶 is in the interior of ∠𝐴𝑂𝐵.)  Angle (union of two different rays sharing a common vertex, e.g., ∠𝐴𝐵𝐶)

Arc (connected portion of a circle)
Collinear (Three or more points are collinear if there is a line containing all of the points; otherwise, the points are non-collinear.)

Complementary angles (two angles with a sum of 90°)

Degree, degree measure of an angle (Subdivide the length around a circle into 360 arcs of equal length.

A central angle for any of these arcs is called a one-degree angle and is said to have an angle measure of 1°. )

Diagonal (straight lines joining two opposite corners of a straight-sided shape) 

Equilateral triangle (triangle with three equal sides)

Figure (set of points in the plane) 

Interior of an angle (the convex1 region defined by the angle)

Intersecting lines (lines that contain at least one point in common) 

Isosceles triangle      (triangle with at least two equal sides)

Length of an arc (circular distance around the arc) 

Line (straight path with no thickness that extends in both directions without end, e.g., 𝐴𝐵 ⃡⃑⃑⃑ ⃑ )

Line of symmetry (line through a figure such that when the figure is folded along the line, two halves are created that match up exactly) 

Line segment (two points, 𝐴 and 𝐵, together with the set of points on 𝐴𝐵 ⃡⃑⃑⃑ ⃑  between 𝐴 and 𝐵, e.g., 𝐴𝐵 ̅̅̅̅) 

Obtuse angle (angle with a measure greater than 90°, but less than 180°) 

Obtuse triangle (triangle with an interior obtuse angle)

Parallel (two lines in a plane that do not intersect, e.g., 𝐴𝐵 ⃡⃑⃑⃑ ⃑  ∥ 𝐶𝐷 ⃡⃑⃑⃑ ⃑ ) 

Perpendicular (Two lines are perpendicular if they intersect, and any of the angles formed between the lines is a 90° angle, e.g., 𝐸𝐹 ⃡⃑ ⃑ ⃑ ⃑  ⊥ 𝐺𝐻 ⃡⃑⃑⃑⃑ .)

Point (precise location in the plane) 

Protractor (instrument used in measuring or sketching angles) 

Ray (The 𝑂𝐴 ⃑⃑⃑⃑⃑  is the point 𝑂 and the set of all points on 𝑂𝐴 ⃡⃑⃑⃑⃑  that are on the same side of 𝑂 as the  point 𝐴.) 

Right angle (angle formed by perpendicular lines, measuring 90°)

Right triangle (triangle that contains one 90° angle)

  Scalene triangle (triangle with no sides or angles equal) 

Straight angle (angle that measures 180°)  

Supplementary angles (two angles with a sum of 180°)

Triangle (A triangle consists of three non-collinear points and the three line segments between them.  The three segments are called the sides of the triangle, and the three points are called the vertices.)

Vertex (a point, often used to refer to the point where two lines meet, such as in an angle or the corner of a triangle)

Vertical angles (When two lines intersect, any two non-adjacent angles formed by those lines are called vertical angles or vertically opposite angles.)