- 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 /.
Meaning of 'ellipticity' (Princeton's WordNet)
1 . ellipticity
[ n]
Meaning (1): - the property possessed by a round shape that is flattened at the poles