Before finding the word that best describes KN, let's review some important definitions about circles.
Radius: A segment whose endpoints are the center and any point on the circumference of a circle.
Chord: A segment whose endpoints are on the circumference of a circle.
Diameter: A chord that contains the center of the circle.
Secant: A line that intersects a circle in two points.
Tangent: A line in the plane of a circle that intersects the circle in exactly one point — the point of tangency.
Now, consider the given diagram.
We can see that KN is a segment whose endpoints are points on the circle. We can also see that this segment contains the center of the circle. Therefore, according to the definitions, we can identify KN as a diameter of the circle.
