The antonyms for the word "un grown" are grown, mature, ripe, developed, seasoned, and established. These words connote the idea of a state of readiness, completeness, and perfection. When someone is described as grown, the person has reached a point of physical, mental, and emotional maturity. Similarly, maturity, development, and establishment imply that something has grown to the fullest extent or has achieved a state of perfection. On the other hand, being ungrown suggests a lack of development, immaturity, or insecurity. The antonyms of un grown thus provide a range of desirable qualities and traits that one could strive towards.