THE SET OF ALL POINTS IN A PLANE THAT ARE THE SAME DISTANCE .

anything having or arranged in the form of a half of a circle .

the outer boundary, especially of a circular area .

any particular extent of space or surface .

a straight line passing through the center of a circle or sphere and meeting the circumference or surface at each end. .

a straight line extending from the center of a circle or sphere to the circumference or surface .

the letter π, used as the symbol for the ratio of the circumference of a circle to its diameter .

a set form of words, as for stating or declaring something definitely or authoritatively, for indicating procedure to be followed, or for prescribed use on some ceremonial occasion.