noun (plural -ties)
Etymology: Middle French opacité shadiness, from Latin opacitat-, opacitas, from opacus shaded, dark
Date: 1560
1. obscurity of sense ; unintelligibleness, the quality or state of being mentally obtuse ; dullness, the quality or state of a body that makes it impervious to the rays of light, an opaque spot in a normally transparent structure (as the lens of the eye)