'Ellipticity' definitions:

Definition of 'ellipticity'

From: WordNet
noun
The property possessed by a round shape that is flattened at the poles; "the oblateness of the planet" [syn: oblateness, ellipticity]

Definition of 'Ellipticity'

From: GCIDE
  • Ellipticity \El`lip*tic"i*ty\, n. [Cf. F. ellipticit['e].] 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 1/29966. [1913 Webster]
  • Note: Some writers use ellipticity as the ratio of the difference of the two semiaxes to the minor axis, instead of the major. --Nichol. [1913 Webster]