ostentation vs ostentatiousness

ostentation and ostentatiousness both are nouns.

Word	Noun	Adjective	Verb	Adverb
ostentation	Yes	No	No	No
ostentatiousness	Yes	No	No	No

As nouns, ostentation and ostentatiousness are synonyms defined as:

ostentation and ostentatiousness: lack of elegance as a consequence of being pompous and puffed up with vanity

Other synonyms of ostentation include inflation, pomposity, pompousness, pretentiousness, puffiness, splashiness.

ostentation (noun)	ostentatiousness (noun)
pretentious or showy or vulgar display	lack of elegance as a consequence of being pompous and puffed up with vanity
lack of elegance as a consequence of being pompous and puffed up with vanity
a gaudy outward display