Circle Vocabulary

Tangent

• A line that intersects a circle at exactly one point

• A line that intersects a circle at two points

• A line that is parallel to the radius of the circle

• A line that does not touch the circle at all

Minor Arc

• An arc with a measure less than 180º

• An arc that is exactly 180º

• An arc that is greater than 180º

• An arc that is a full circle

Inscribed Angle

• An angle with a vertex on the circle and two sides that are chords

• An angle formed by two tangents to the circle

• An angle whose vertex is outside the circle

• An angle formed by a secant and a tangent to the circle

Diameter

• A chord that passes through the center of the circle

• A line segment connecting two points on the circle

• The distance across the circle measured through the center

• A line that touches the circle at one point

Major Arc

• An arc with a measure less than 90º

• An arc with a measure equal to 180º

• An arc with a measure greater than 180º

• An arc that is a semicircle

Chord

• A segment with endpoints on the circle

• A line that touches the circle at one point

• A segment that passes through the center of the circle

• A polygon inscribed in the circle

Central Angle

• An angle with a vertex at the center and two sides that are radii

• An angle formed by two tangents to a circle

• An angle whose vertex is on the circumference of a circle

• An angle that measures more than 180 degrees

Radius

• A segment whose endpoints are the center and any point on the circle

• A line that connects two points on the circle

• The distance from the center to the circumference

• A segment that passes through the center of the circle

Arc

• A portion of the edge of the circle defined by two endpoints

• A line segment that connects two points on a circle

• The center point of a circle

• A complete rotation around a circle

Semicircle

• An arc with endpoints that are the endpoints of a diameter (equals 180º)

• A full circle with a radius of 1 unit

• A line segment that connects two points on a circle

• An arc that measures less than 90º