(1):

(n.) The faculty of nice discernment or perception; acumen; keenness; sharpness; sensitiveness; - applied to the senses, or the understanding. By acuteness of feeling, we perceive small objects or slight impressions: by acuteness of intellect, we discern nice distinctions.

(2):

(n.) Shrillness; high pitch; - said of sounds.

(3):

(n.) Violence of a disease, which brings it speedily to a crisis.

(4):

(n.) The quality of being acute or pointed; sharpness; as, the acuteness of an angle.