(gearing) The outline of the smallest cross section of a hyperboloid of revolution.

(mathematics) A minimum circle on a surface of revolution, cut out by a plane perpendicular to the axis.

plural of Carlyle circle

(mathematics) A certain circle in a coordinate plane associated with a quadratic equation, having the property that the solutions of the equation are the horizontal coordinates of the intersections of the circle with the horizontal axis.

plural of circle of Willis

plural of polar circle

(astronomy) A great circle on the celestial sphere, perpendicular to the horizon, that passes through the zenith and nadir

(education) Time spent by a group sitting together to take part in an activity.

plural of circle time

(geometry) A circumcircle.