means The quality of having a fine edge or point, or by extension a keenness of mind, vision, taste, or tone that cuts or registers cleanly.

from From Old English 'scearp' (cutting, keen), the same root that gives us 'sharp' itself — a Germanic word with cousins in Dutch 'scherp' and German 'scharf,' all tracing back to a Proto-Germanic sense of cutting or scraping. The suffix '-ness,' another old English workhorse, simply turns the adjective into the quality itself. So 'sharpness' is, quite literally, the state of being able to cut — a meaning that long ago slipped from blades into wits, eyes, and words.