ellipticity vs bulginess

ellipticity and bulginess both are nouns.

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

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

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

Other hypernyms of ellipticity include roundedness.

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