How would you describe someone showing no care or concern in attitude or action?

The term "indifferent" refers to a lack of interest, concern, or sympathy towards something or someone. When someone is described as indifferent, it highlights their attitude of apathy or nonchalance, indicating that they do not care about the situation at hand. This term captures the essence of showing no care or concern effectively, making it the most suitable choice for the description provided.

The other options do not convey the same meaning. "Miserly" refers to someone who is stingy or reluctant to spend money, which does not relate to a general lack of concern or care. "Penchant" describes a strong liking or inclination toward something, which is the opposite of indifference. Finally, "frugality" pertains to being economical or thrifty, often in the context of managing resources wisely, rather than an apathetic attitude. Hence, "indifferent" stands out as the clear choice for someone demonstrating no care or concern.