ellipticity vs roundedness

ellipticity and roundedness both are nouns.

Word	Noun	Adjective	Verb	Adverb
ellipticity	Yes	No	No	No
roundedness	Yes	No	No	No

As nouns, roundedness is a hypernym of ellipticity; that is, roundedness is a word with a broader meaning than ellipticity:

ellipticity: the property possessed by a round shape that is flattened at the poles
roundedness: the property possessed by a rounded convexity

Other hypernyms of ellipticity include bulginess.

ellipticity (noun)	roundedness (noun)
the property possessed by a round shape that is flattened at the poles	the property possessed by a rounded convexity