Acuity refers to sharpness or keenness, especially of the senses or mind. Someone with high visual acuity can see tiny details clearly from far away: they might spot a hawk circling high overhead when everyone else sees just a speck. A person with excellent mental acuity thinks quickly and grasps complex ideas easily.

The word comes from Latin acuere, meaning “to sharpen.” Think of acuity as the opposite of dullness: it's that quality of being finely tuned and precisely focused, whether you're looking at something, listening to something, or thinking about something.