Which term describes the action of making something less bright or strong?

The term that describes the action of making something less bright or strong is "dim." When something is dimmed, such as light, it becomes less intense or less vivid. This term specifically connotes a reduction in brightness and is commonly used in contexts like lighting or colors.

While "reduce" can imply a lowering in amount or intensity of something, it does not specifically pertain to brightness. "Weaken" typically refers to a decrease in strength or effectiveness rather than brightness. Similarly, "lower" can describe making something smaller or less in quantity but doesn't inherently relate to brightness in the way "dim" does. Therefore, "dim" is the most precise term for the action of making something less bright.