To make smaller or less:
* Reduce: This is a general synonym, meaning to make something smaller in size, amount, or degree.
* Decrease: Similar to reduce, but often used for a gradual decline.
* Lessening: A more formal and literary synonym for decrease.
* Shrink: To become smaller in size, often used for physical objects.
* Abate: To become less intense or severe, often used for things like pain or anger.
* Subside: To become less strong or active, often used for things like storms or emotions.
To make less important or valuable:
* Depreciate: To decrease in value, often used for financial assets.
* Devalue: To reduce the worth or importance of something.
* Undermine: To weaken or damage something gradually.
* Impair: To weaken or damage something, often used for abilities or functions.
To make less powerful or effective:
* Weaken: To make something weaker.
* Sap: To drain or exhaust something, often used for energy or resources.
* Curtail: To shorten or limit something, often used for activities or rights.
To make less prominent or noticeable:
* Fade: To become less bright or clear, often used for colors or memories.
* Dwindle: To become gradually smaller, often used for numbers or resources.
* Wane: To decrease in size or strength, often used for the moon.
The best synonym for "diminish" depends on the specific context and the specific effect you want to convey.