Machinery. the distance between the centers of two cylindrical objects one of which surrounds the other, as between an eccentric and the shaft on which it is mounted.

Mathematics. a constant expressed as the ratio of the distance from a point on a conic to a focus and the distance from the point to the directrix.

noun plural -ties

unconventional or irregular behaviour

deviation from a circular path or orbit

a measure of the noncircularity of an elliptical orbit, the distance between the foci divided by the length of the major axis

geometry a number that expresses the shape of a conic section: the ratio of the distance of a point on the curve from a fixed point (the focus) to the distance of the point from a fixed line (the directrix)

the degree of displacement of the geometric centre of a rotating part from the true centre, esp of the axis of rotation of a wheel or shaft

n.

1540s, of planetary orbits; 1650s, of persons (an instance of eccentricity); 1794, of persons (a quality of eccentricity); from eccentric (adj.) + -ity. Related: Eccentricities.

A measure of the deviation of an elliptical path, especially an orbit, from a perfect circle. It is equal to the ratio of the distance between the foci of the ellipse to the length of the major axis of the ellipse (the distance between the two points farthest apart on the ellipse). Eccentricity ranges from zero (for a perfect circle) to values approaching 1 (highly elongated ellipses).

The ratio of the distance of any point on a conic section from a focus to its distance from the corresponding directrix. This ratio is constant for any particular conic section.