The word "un-ostentatiousnesses" refers to a lack of showiness or pretentiousness. Its antonyms, on the other hand, include words such as grandiose, flamboyant, pompous, luxurious, and extravagant. These words denote the opposite of simplicity and humility, and instead suggest something that is elaborate, showy, and opulent. A person who is ostentatious tends to seek attention and admiration through extravagant displays of wealth or status, whereas un-ostentatiousness denotes a lack of such desires. Therefore, using antonyms to "un-ostentatiousness" can help us describe people or things that are characterized by extravagance, grandeur, or showiness.