General opposites:
* Moderate: This is a very common antonym, suggesting something in the middle ground.
* Mild: Similar to moderate, but can also suggest a lack of intensity.
* Temperate: Suggests a balanced or controlled state.
* Normal: Represents the typical or expected level.
Opposites related to intensity:
* Slight: Indicates a very low level of intensity.
* Minimal: Meaning the least possible amount or degree.
* Negligible: So small or insignificant as to be disregarded.
Opposites related to position:
* Central: Refers to the middle or center point.
* Average: Represents the typical value or level.
Opposites related to behavior:
* Cautious: Suggests carefulness and avoiding risks.
* Reasonable: Implies a balanced and logical approach.
The best antonym for "extreme" will depend on the specific situation and the meaning you want to convey.