Some common words used specifically in geometry are "perpendicular," "vertex," "obtuse," "scalene" and "diameter." Other terms often used in geometry are "arc," "cylinder," "hypotenuse," "ordered pair" and "y-intercept."
"Perpendicular" refers to two line segments that form 90-degree angles when they cross. Ninety-degree angles are also called "right angles" in geometry. "Vertex" is the name of the intersection point of two sides of a shape. This term is often used interchangeably with "angle."
"Obtuse" is a word applied to an angle greater than 90 degrees but less than 180 degrees. This word's counterpart is "acute," which applies to an angle less than 90 degrees but greater than zero degrees. "Scalene" is the word used for a triangle with three unequal sides and angles. This word is associated with "isosceles," which refers to a triangle with two equal sides, and "equilateral," which refers to a triangle with all equal sides.
"Diameter" is the name of a line segment that begins and ends on points along the circle's circumference while passing through the center of a circle. "Arc" is the name of a section of a circle's circumference. "Hypotenuse" refers to the longest side of a right triangle.
"Ordered pair" is the name of a group of two-dimensional coordinates given in parentheses. "Y-intercept" is the name of the point at which a line intersects the y-axis on a coordinate plane.