Give a definition for the radius of a circle. Are there other terms that need to be defined first? What are they,and how might you define them?

(N/A) Definition of the radius of a circle:
The distance from the center to a point on the circle is called the radius of the circle. In the figure,$P$ is the center and $Q$ is a point on the circle,then the line segment $PQ$ is the radius.
Other terms that need to be defined first:
$1$. Circle: $A$ circle is the set of all points in a plane that are at a fixed distance from a fixed point in the plane.
$2$. Center: The fixed point from which all points on the circle are at a fixed distance is called the center of the circle.
$3$. Point: $A$ point is that which has no part.
$4$. Plane: $A$ plane is a surface which lies evenly with the straight lines on itself.