Antonyms for the word "not extreme" may include moderate, average, ordinary, commonplace, run-of-the-mill, and standard. These words imply a lack of excessiveness or extremity, and instead suggest a more balanced, reasonable approach. Some other antonyms that convey a similar meaning include conservative, mild, tempered, controlled, and restrained. Generally, these terms reflect a more measured perspective, and suggest a desire for moderate action or behavior. By contrast, extreme antonyms like radical, unconventional, and adventurous often suggest a willingness to take risks or challenge established norms. Overall, the choice of antonym will depend on the context and the individual's intended meaning.