Excess
For extreme (immoderate), the opposite would be moderate, limited, or mild. For extreme (extraordinary), the opposite would be average, ordinary, or tame. For extreme (severe), the opposite would be mild, slight, or minimal.
Moderate as an adjective means average in quality, intensity, amount, or degree. As the opposite of this definition of moderate would be extreme, moderate and extreme are antonyms.
calm, moderate, small, unpretentious
Extreme Excessive
cheap, thrifty, moderate, plain
insignificant or moderate
Light, moderate, or soft may all be used as antonyms depending of the circumstances.
The opposite is a calm sea. Other words could be placid, moderate, gentle, tranquil, etc.
opposites: cheerful, elated, excited, exhilarated, happy, pleased , calm, mild, moderate, peaceful, quiet
Extremist is extreme, moderate is moderate.
You use moderate to describe people or groups who have moderate political opinions or policies.
The Abbrevition for Moderate is Mo