The perimeter of a circle is its circumference
It's called a radius
circumference
That is called an "arc".
It is called a protractor.
The circle on top of an i is called a dot. That is why you hear teachers talk about dotting i's.
The center of a circle is called the origin. It is a point at one end of a radius, the other end of which defines the circumference of the circle.
I bi I believe it is called a Sphere
A chord. The longest possible chord is one that goes through the center of the circle. That has a special name ... it's called the 'diameter' of the circle.
It is called a cone.
It is just called a "central angle".
That's called the radius.