What is the term for the attribute of being brief or fleeting?

The term that describes the attribute of being brief or fleeting is "Brevity." This word specifically refers to the quality of expressing much in few words, which relates directly to the concept of something being concise or short-lived. In various contexts, brevity is not only associated with language and communication but can also imply the transient nature of experiences or moments, emphasizing their fleeting characteristic.

The other options, while they have their own meanings, do not capture the essence of being brief. For instance, "Circumspect" pertains to being cautious or considering all possible consequences before acting, rather than brevity. "Disabuse" means to clarify or free someone from a misconception, focusing instead on enlightenment rather than briefness. "Eloquent" describes the ability to express oneself clearly and elegantly, often in a way that is not necessarily brief. Thus, the choice of "Brevity" accurately reflects the intended meaning of being brief or fleeting.