What term best describes the quality of being keen or sharp-witted?

The term that best describes the quality of being keen or sharp-witted is perceptiveness. This word conveys a deep understanding and insight, indicating someone who is able to notice and comprehend things clearly and quickly. A perceptive person often has a sharp intellect, enabling them to grasp nuances and subtleties in various situations, which aligns well with the notion of being keen or sharp-witted.

In contrast, clarity refers to the quality of being clear or easy to understand, which does not explicitly capture sharp-wittedness. Complexity pertains to the intricacy or difficulty of something, which does not directly relate to the sharpness of wit or intelligence. Lastly, simplicity denotes the state of being simple or uncomplicated, contrasting with the idea of having a sharp or keen understanding.