extravagance vs extravagancy

extravagance and extravagancy both are nouns.

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

As nouns, extravagance and extravagancy are synonyms defined as:

extravagance and extravagancy: the quality of exceeding the appropriate limits of decorum or probability or truth

extravagance (noun)	extravagancy (noun)
the activity of excessive spending	the quality of exceeding the appropriate limits of decorum or probability or truth
the trait of spending extravagantly
the quality of exceeding the appropriate limits of decorum or probability or truth