ELLIPTICITY

oblateness, ellipticity

(noun) the property possessed by a round shape that is flattened at the poles; “the oblateness of the planet”

Source: WordNet® 3.1

Etymology

Noun

ellipticity (countable and uncountable, plural ellipticities)

(uncountable) The condition of being elliptical (flattened from perfect circular or spherical form)

(countable, mathematics) A measure of this flattening that is a function of the ellipse's equatorial and polar radii

Source: Wiktionary

El`lip*tic"i*ty, n. Etym: [Cf. F. ellipticité.]

Definition: Deviation of an ellipse or a spheroid from the form of a circle or a sphere; especially, in reference to the figure of the earth, the difference between the equatorial and polar semidiameters, divided by the equatorial; thus, the ellipticity of the earth is

Note: Some writers use ellipticity as the ratio of the difference of the two semiaxes to the minor axis, instead of the major. Nichol.

Source: Webster’s Unabridged Dictionary 1913 Edition