OPACITY

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)