"Adultness" is a noun that describes the state or quality of being an adult. However, like all words, its meaning has opposite words known as antonyms. The opposite of adultness could be childhood, which refers to the state or quality of being a child. Or, it could be immaturity, which is the lack of emotional or intellectual maturity. Adolescence could also be an antonym of adultness, which refers to the transitional stage between childhood and adulthood. In contrast, senility, which is the deterioration of mental or physical abilities, could also be considered an antonym of adultness. Therefore, it is vital to understand antonyms as they contribute to a better understanding of any word's meaning.