The word "un extreme" can be difficult to find antonyms for, as it is a negation of the word "extreme". However, there are several words that can be used as antonyms depending on the context. For example, "moderate" or "balanced" could be used to refer to something that is not extreme in its nature. Alternatively, "mild" or "average" could be used to describe something that is not at either end of a spectrum. In a more figurative sense, "harmony" or "equilibrium" could be used to describe a state of balance, rather than one of extremes. Ultimately, the antonym of "un extreme" will depend on the specific context in which it is used.