The word un-ostentatiousness refers to the quality of being unpretentious or modest. Its antonyms, on the other hand, are associated with flamboyance, showiness, and extravagance. Some of the antonyms for un-ostentatiousness include grandiosity, ostentation, pomp, splendor, pretentiousness, exhibitionism, flamboyance, and extravagance. These words are used to describe things or people that are very extravagant, showy, and ostentatious in their behavior or appearance. They are often associated with people who are seeking attention, status, or approval through their display of wealth or superiority. In contrast, un-ostentatiousness implies a sense of humility, simplicity, and sincere modesty.