extravagancy vs excessiveness

extravagancy and excessiveness both are nouns.

Word	Noun	Adjective	Verb	Adverb
extravagancy	Yes	No	No	No
excessiveness	Yes	No	No	No

As nouns, excessiveness is a hypernym of extravagancy; that is, excessiveness is a word with a broader meaning than extravagancy:

extravagancy: the quality of exceeding the appropriate limits of decorum or probability or truth
excessiveness: immoderation as a consequence of going beyond sufficient or permitted limits

Other hypernyms of extravagancy include excess, inordinateness.

extravagancy (noun)	excessiveness (noun)
the quality of exceeding the appropriate limits of decorum or probability or truth	immoderation as a consequence of going beyond sufficient or permitted limits