What does opacity mean?
Opacity is the quality of not letting light pass through, or more generally, of preventing people from seeing, understanding, or reaching what lies beneath a surface. A material with high opacity blocks much of the light that reaches it, while a transparent material has low opacity. The word also has an important figurative use: an opaque decision, process, or agreement is one whose reasoning or details are difficult to perceive. In science and media, opacity can be measured numerically, describing the proportion of light or radiation that is blocked or absorbed. This makes the term useful wherever visibility is incomplete, whether the subject is glass, a cloud, a photograph, or a complicated institutional procedure. Opacity is especially associated with lack of transparency and can imply concealment, complexity, or an unwillingness to provide clear explanations, although it does not necessarily suggest deliberate secrecy.
nounThe quality of being opaque, especially the degree to which a material or substance allows light to pass through it. By extension, it refers to obscurity, incomprehensibility, or lack of transparency.
- The quality of being opaque; the degree to which a material, substance, image, or surface prevents light from passing through.
- The quality of being obscure, difficult to understand, or resistant to disclosure.
- A quantitative measure of how much light passes through a material, used especially in physics, astronomy, and imaging.
"The fog reduced the landscape to a soft veil of near total opacity."
"The dense cloud has an opacity that completely hides the mountains."
"The report was criticized for the opacity of its financial disclosures."
Usually plural when referring to different measurable values or distinct instances of opacity.
"The researchers compared the opacities of clouds at different altitudes."
Opacity began with a Roman idea of darkness: the Latin opacus described something shaded or closed to light, and the word still measures how much of the world can be seen through.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does opacity come from?
Opacity entered English through French opacité, from Latin opacitas, a noun derived from opacus, meaning “opaque” or “dark.” The Latin adjective is related to opaque, which entered English through French opaque. Later English forms such as opacify and opacification were developed for the process of becoming opaque and the result of making something opaque.
Related word forms
How opacity is actually used
In technical contexts, especially astronomy and image processing, opacity often refers to a numerical quantity describing the extent to which light is blocked or attenuated. In figurative use, it describes something deliberately or unintentionally difficult to understand, such as legal language, organizational decisions, or negotiations.