It is called a tangent segment.
A tangent line to a circle is a line that touches the circle at exactly one point, known as the point of tangency. The diameter of the circle is the longest chord, passing through the center and connecting two points on the circle. At the point of tangency, the tangent line is perpendicular to the radius drawn to that point, and in the case of the diameter, the radius at the endpoint of the diameter is also perpendicular to the tangent line. Thus, while a diameter can relate to tangents by touching the circle at endpoints, they serve different geometric roles.
A tangent of a circle is a straight line that touches the circle at only one point.
A Chord
radius
The tangent secant angle is the angle between the tangent to a circle and the secant, when the latter is extended.
A line segment drawn through the centre of a circle and having endpoints on the circumference of that circle is called the diameter. Notably, a line segement with one endpoint at the centre of the circle and one anywhere on the circumference of the circle is called the radius, and is exactly half the length of the diameter.
Perpendicular lines
A tangent of a circle is a straight line that touches the circle at only one point.
The Tangent Line to Circle Theorem states that a line is tangent to a circle if and only if it's perpendicular to the circle's radius.
A chord in which the diameter is the largest
A Chord
diameter
radius
The segment you describe is the radius of the circle.
Such a line is called a tangent line or a tangent to the circle. [Tangent is Latin for touching-- a tangent line touches the circle at just one point. ]
The tangent secant angle is the angle between the tangent to a circle and the secant, when the latter is extended.
Is called a radius.