ostentation vs pretentiousness

ostentation and pretentiousness both are nouns.

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

As nouns, pretentiousness is a hypernym of ostentation; that is, pretentiousness is a word with a broader meaning than ostentation:

ostentation: pretentious or showy or vulgar display
pretentiousness: the quality of being pretentious (behaving or speaking in such a manner as to create a false appearance of great importance or worth)

Other hypernyms of ostentation include largeness, pretension.

As nouns, ostentation and pretentiousness are synonyms defined as:

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

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

ostentation (noun)	pretentiousness (noun)
pretentious or showy or vulgar display	the quality of being pretentious (behaving or speaking in such a manner as to create a false appearance of great importance or worth)
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