Which of the following terms refers to injuring someone's reputation?

The term that refers to injuring someone's reputation is "discredit." This word signifies the act of harming someone's good name or diminishing their credibility. Discrediting can occur through negative remarks, spreading false information, or highlighting failures in a manner that tarnishes a person's reputation.

In contrast, the other terms do not relate to reputation in the same way. Disinterest refers to a lack of interest in something, which has no bearing on a person's reputation. Disproof relates to proving something as false or incorrect, typically in a logical or scientific context, rather than focusing on reputational harm. Dismal describes a state of being gloomy or depressing, which also does not connect directly with issues of reputation. Therefore, "discredit" is the most accurate term for the action of harming someone's reputation.