The antonyms for the word "un-grown" include grown-up, mature, adult, developed, and full-grown. These words signify the state of being fully developed and mature, whereas "un-grown" refers to something that is not yet fully developed or immature. For instance, a plant that has not fully grown is considered un-grown, while a fully developed plant is full-grown. Similarly, a child is considered un-grown and gradually develops into a grown-up or adult. The use of antonyms enhances the effectiveness of communication by allowing speakers or writers to convey meaning in a clear, explicit, and concise manner.