What term describes a lack of sensitivity, showing indifference to the feelings of others?

The term that best describes a lack of sensitivity and indifference to the feelings of others is "callous." This word conveys a sense of emotional detachment or insensitivity, where an individual may disregard the emotional states or needs of others. A callous person often shows little to no empathy, highlighting their disinterest in the feelings or suffering of those around them.

The other choices do not convey this indifference. "Benign" refers to something that is gentle and kindly, often suggesting a harmless or positive nature. "Benevolent" implies a disposition to do good and show kindness, which is the opposite of lacking sensitivity. "Candid" describes someone who is truthful and straightforward, which does not relate to emotional insensitivity at all. Thus, "callous" is the most accurate descriptor in this context.