opac·i·ty | \ ō-ˈpa-sə-tē \
plural opacities

Definition of opacity 

1a : obscurity of sense : unintelligibility

b : the quality or state of being mentally obtuse : dullness

2 : the quality or state of a body that makes it impervious to the rays of light broadly : the relative capacity of matter to obstruct the transmission of radiant energy

3 : an opaque spot in a normally transparent structure (such as the lens of the eye)

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Examples of opacity in a Sentence

the opacity of the glass Critics have noted the opacity of her writing style.

Recent Examples on the Web

Though journalists have long criticized the EPA under Obama and George W. Bush for a lack of transparency, Pruitt's tenure was marked by an unprecedented opacity. Dino Grandoni, Washington Post, "The Energy 202: The EPA won't change policy after Pruitt. But it might be more transparent about it.," 10 July 2018 Forster captures the complexity of Indian society with its vying religions and languages, creating an opacity frustrating to the British Raj. John Timpane, Philly.com, "'Passage' at the Wilma Theater: E.M. Forster must be turning in his grave," 26 Apr. 2018 Each book ends up a meditation on the opacity of class experience, to those who live in it but also to those who theorize it. Jedediah Purdy, The New Republic, "The Remaking of Class," 27 June 2018 Romantic love doesn’t lessen the opacity of other people’s thoughts and motivations. refinery29.com, "Read This & You’ll Never Hear “...Baby One More Time” The Same Way Again," 26 June 2018 While investors are starved for growth and returns after years of low interest rates, the opacity in metal prices and fickle market sentiment are keeping some away even as large companies like SoftBank Group Corp. and Tesla Inc. make investments. Amrith Ramkumar, WSJ, "Want to Invest in Lithium and Cobalt? Good Prices Are Hard to Find," 19 June 2018 The opacity continued to increase steadily, hitting 10.8 by June 10—enough to block nearly all sunlight. Jay Bennett, Popular Mechanics, "NASA Optimistic That Opportunity Can Survive Martian Dust Storm," 13 June 2018 By the following day, the opacity of the storm (a technical measure of how much light it blocks) had reached record levels, such that Opportunity's instruments could no longer measure it effectively. John Timmer, Ars Technica, "Massive Martian dust storm has put Opportunity rover in a low-power sleep," 13 June 2018 The previous storm had an opacity level, or tau, of 5.5. David Grossman, Popular Mechanics, "NASA's Opportunity Rover Is Heroically Riding Out an Enormous Martian Storm," 11 June 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'opacity.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of opacity

1575, in the meaning defined at sense 1a

History and Etymology for opacity

Middle French opacité shadiness, from Latin opacitat-, opacitas, from opacus shaded, dark

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Statistics for opacity

Last Updated

14 Sep 2018

Look-up Popularity

Time Traveler for opacity

The first known use of opacity was in 1575

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English Language Learners Definition of opacity

: the quality of a material that does not allow light to pass through it : the quality of being opaque

: the quality of being difficult to understand or explain


opac·i·ty | \ ō-ˈpas-ət-ē \
plural opacities

Medical Definition of opacity 

1 : the quality or state of a body that makes it impervious to the rays of light broadly : the relative capacity of matter to obstruct by absorption or reflection the transmission of radiant energy (as X-rays, infrared radiation, or sound)

2 : an opaque spot in a normally transparent structure (as the lens of the eye)

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Comments on opacity

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an open space surrounded by woods

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