The quality of being opaque, or not allowing light to pass through. The opacity of the glass made it impossible to see through.
The degree to which something reduces the passage of light. The opacity of the fog was so high that visibility was reduced to a few meters.
The state of being difficult to understand or unclear. The opacity of the legal document made it challenging for the layperson to comprehend.
An opaque area visible on a radiograph or similar imaging study, indicating a region through which radiation does not readily pass. The chest X-ray showed a round opacity in the upper lobe.