What does 'impair' refer to in general usage?

The term "impair" generally refers to causing damage or detriment to something, which aligns with the meaning of "to harm." In a broader context, it suggests a reduction in quality, strength, or effectiveness. For example, if someone's ability to think clearly is impaired, their cognitive functions are somehow diminished or harmed.

This understanding reinforces why "to harm" is the most suitable choice. The other options, including "to strengthen," "to make better," and "to develop," convey positive outcomes, which directly contradict the essence of "impair," as impairing something inherently reduces its value or functionality. Thus, recognizing that impairment implies a negative impact clarifies why "to harm" is the accurate definition.