The antonyms for the word "un ostentatious" are "flashy," "showy," "pretentious," "exaggerated," and "ostentatious." If an item or a person is not ostentatious, it means they are modest, humble, and not extravagant. Modesty and simplicity are highly valued in many cultures, and unostentatious behavior is often seen as a sign of good character. People who are unostentatious do not seek attention or recognition for themselves and prefer to live a simple life. In contrast, ostentatious people tend to flaunt their wealth, status, and achievements, often in an exaggerated manner, to gain admiration and attention.